Question Kunena 5.2.8 + clean J3 + T4 framework + BS 4 template = edit not working

Hi!
I had a recent post here describing the same problem but I could not get help there as I used a Bootstrap 5 template.

I have now installed
- a fresh and clean Joomla 3.10.5
- Kunena 5.2.8
- Joomlart's T4 framework in the latest version 2.1.1
- Joomlart's T4 Blank Default template (which uses Bootstrap 4)

Kunena is in the default configuration and shows all categories. However posting (and also editing) is not possible. It just causes a white / blank page.

Thanks!

Kind regards,
Frank

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Kunena menu details:

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ID	Name	Menutype	Link	Path	In trash
116	Forum	kunenamenu	view=home&defaultmenu=118	forum	No
117	Index	kunenamenu	view=category&layout=list	forum/index	No
118	Recent Topics	kunenamenu	view=topics&mode=replies	forum/recent	No
119	Unread	kunenamenu	view=topics&layout=unread	forum/unread	No
120	New Topic	kunenamenu	view=topic&layout=create	forum/newtopic	No
121	No Replies	kunenamenu	view=topics&mode=noreplies	forum/noreplies	No
122	My Topics	kunenamenu	view=topics&layout=user&mode=default	forum/mylatest	No
123	Profile	kunenamenu	view=user	forum/profile	No
124	Help	kunenamenu	view=misc	forum/help	No
125	Search	kunenamenu	view=search	forum/search	No
126	Forum	mainmenu	Itemid=116	kunena-2022-01-28	No

Joomla default template details : t4_blank | author: JoomlArt | version: 1.1.4 | creationdate: January 14, 2022

Kunena default template details : Crypsisb4 | author: Kunena Team | version: 5.2.8 | creationdate: 2022-01-01

Kunena template params:

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DefaultCategoryicon
profileIconset	default
DefaultIconset	default
editorIconset	default
borderless	1
tooltips	1
SubjectLengthMessage	80
fullactions	1
quick	0
displayMenu	1
displayDropdownMenu	1
displayDropdownContent	1
displayModule	1
displayBreadcrumb	1
displayAnnouncement	1
displayFooter	1
avatarPosition	left
formRecover	0
labels	0
whoisonlineName	default
avatarType	rounded
topicicontype	fa
fontawesome	0
fontawesome_layer_v4	0
icons	0
socialshare	0
socialsharetag
socialtheme	classic
optional_username	0
writeaccess	0
localstorage	0
IconColor	inherit
IconColorNew	#48a348
editor	0
Bold	1
Italic	1
Underline	1
Strike	1
Subscript	1
Superscript	1
RemoveFormat	1
BulletedList	1
NumberedList	1
Blockquote	1
JustifyLeft	1
JustifyCenter	1
JustifyRight	1
JustifyBlock	1
Link_Unlink	1
Image	1
Smiley	1
Confidential	1
Hidetext	1
Spoiler	1
Code	1
Ebay	1
Twitter	1
Instagram	1
Soundcloud	1
FontSize	1
TextColor	1
Maximize	1
Map	1
Video	1
ckeditorParams
wysibbParams
nameskinckeditor
ckeditorcustomprefixconfigfile
avatarSizeX	40
avatarSizeY	90
avatarSizeXThumb	36
avatarSizeYThumb	36
avatarSizeXWelcome	72
avatarSizeYWelcome	72
avatarSizeXList	36
avatarSizeYList	36
avatarSizeXPost	144
avatarSizeYPost	144
avatarSizeXProfile	200
avatarSizeYProfile	200
templatebyText
templatebyName
templatebyLink

Kunena version detailed: Kunena 5.2.8 | 2022-01-01 [ Alcora ]
        | Kunena detailed configuration:

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Kunena config settings:
board_offline	0
enablerss	1
threads_per_page	20
messages_per_page	6
messages_per_page_search	15
showhistory	1
historylimit	6
shownew	1
disemoticons	0
template	crypsisb4
showannouncement	1
avataroncat	0
catimagepath	category_images
showchildcaticon	1
rtewidth	450
rteheight	300
enableforumjump	1
reportmsg	1
username	1
askemail	0
showemail	0
showuserstats	1
showkarma	1
useredit	1
useredittime	0
useredittimegrace	600
editmarkup	1
allowsubscriptions	1
subscriptionschecked	1
allowfavorites	1
maxsubject	50
maxsig	300
regonly	0
pubwrite	0
floodprotection	0
mailmod	0
mailadmin	0
captcha	0
mailfull	1
allowavatarupload	1
allowavatargallery	1
avatarquality	75
avatarsize	2048
imageheight	800
imagewidth	800
imagesize	150
filetypes	txt,rtf,pdf,zip,,tgz,
filesize	120
showranking	1
rankimages	1
userlist_rows	30
userlist_online	1
userlist_avatar	1
userlist_posts	1
userlist_karma	1
userlist_email	0
userlist_joindate	1
userlist_lastvisitdate	1
userlist_userhits	1
latestcategory	0
showstats	1
showwhoisonline	1
showgenstats	1
showpopuserstats	1
popusercount	5
showpopsubjectstats	1
popsubjectcount	5
showspoilertag	1
showvideotag	1
showebaytag	1
trimlongurls	1
trimlongurlsfront	40
trimlongurlsback	20
autoembedyoutube	1
autoembedebay	1
ebaylanguagecode	en-us
sessiontimeout	1800
highlightcode	0
rss_type	topic
rss_timelimit	month
rss_limit	100
rss_included_categories
rss_excluded_categories
rss_specification	rss2.0
rss_allow_html	1
rss_author_format	name
rss_author_in_title	1
rss_word_count	0
rss_old_titles	1
rss_cache	900
defaultpage	recent
default_sort	asc
sef	1
showimgforguest	1
showfileforguest	1
pollnboptions	4
pollallowvoteone	1
pollenabled	1
poppollscount	5
showpoppollstats	1
polltimebtvotes	00:15:00
pollnbvotesbyuser	100
pollresultsuserslist	1
allow_user_edit_poll	0
maxpersotext	50
ordering_system	mesid
post_dateformat	ago
post_dateformat_hover	datetime
hide_ip	1
imagetypes	jpg,jpeg,gif,png
checkmimetypes	1
imagemimetypes	image/jpeg,image/jpg,image/gif,image/png
imagequality	50
thumbheight	32
thumbwidth	32
hideuserprofileinfo	put_empty
boxghostmessage	0
userdeletetmessage	0
latestcategory_in	1
topicicons	1
debug	0
catsautosubscribed	0
showbannedreason	0
showthankyou	1
showpopthankyoustats	1
popthankscount	5
mod_see_deleted	0
bbcode_img_secure	text
listcat_show_moderators	1
lightbox	1
show_list_time	720
show_session_type	2
show_session_starttime	1800
userlist_allowed	1
userlist_count_users	1
enable_threaded_layouts	0
category_subscriptions	post
topic_subscriptions	every
pubprofile	1
thankyou_max	10
email_recipient_count	0
email_recipient_privacy	bcc
captcha_post_limit	0
image_upload	registered
file_upload	registered
topic_layout	flat
time_to_create_page	1
show_imgfiles_manage_profile	1
hold_newusers_posts	0
hold_guest_posts	0
attachment_limit	8
pickup_category	0
article_display	intro
send_emails	1
fallback_english	1
cache	1
cache_time	60
iptracking	1
rss_feedburner_url
autolink	1
access_component	1
statslink_allowed	1
superadmin_userlist	0
legacy_urls	0
attachment_protection	0
categoryicons	1
avatarresizemethod	1
avatarcrop	0
user_report	1
searchtime	365
teaser	0
ebay_language	0
ebay_cert_id
allow_change_subject	1
max_links	6
read_only	0
ratingenabled	0
url_subject_topic	0
log_moderation	0
attach_start	0
attach_end	14
attachment_utf8	1
autoembedsoundcloud	1
emailheader	media/kunena/email/
user_status	1
signature	1
personal	1
social	1
plain_email	0
moderator_permdelete	0
avatartypes	gif, jpeg, jpg, png
smartlinking	0
defaultavatar
defaultavatarsmall	s_
quickreply	1
avataredit	0
activemenuitem
mainmenu_id
home_id
index_id
moderators_id
topiclist_id
misc_id
profile_id
search_id
avatar_type	1
sef_redirect	1
allow_edit_poll	1
use_system_emails	0
autoembedinstagram	1
disable_re	0
email_sender_name
display_filename_attachment	0
new_users_prevent_post_url_images	0
minimal_user_posts_add_url_image	10

| Kunena integration settings:

Warning: Spoiler!

Kunena - Finder Disabled
 Kunena - AltaUserPoints Disabled
 Kunena - Community Builder Disabled
 Kunena - Easyblog Disabled
 Kunena - Easyprofile Disabled
 Kunena - Easysocial Disabled
 Kunena - Gravatar Disabled
 Kunena - JomSocial Disabled
 Kunena - Joomla Enabled:  access=1  login=1  
 Kunena - Kunena Enabled:  avatar=1  profile=1  
 Kunena - UddeIM Disabled

| Joomla! detailed language files installed:

Warning: Spoiler!

Joomla! languages installed:
de-DE	German (Germany)
en-GB	English (United Kingdom)

Third-party components: None

Third-party SEF components: None

Plugins: None

Modules: None

I tried this t4 blank template and confirm this error. There is a conflict between this template and Kunena, but unfortunately I am not able to find the cause.