Error after 3.10.3 - 4.0.4 migration: can't navigate articles anymore after upgrade

I have succesfully completed Joomla migration, I can access both backend and frontend of upgraded site, but I get this error while navigating an article on frontend:

Call to undefined method Joomla\CMS\Document\HtmlDocument::addScriptVersion()

I'm using a Yootheme template, but I get the same error when switching to CASSIOPEIA Joomla standard one

I'm also getting this PHP error message when displaying on frontend  only one of the used content categoriers I have on that site:

Exception {#17 #message: "Failed to start application" #code: 500 #file: "./libraries/src/Factory.php" #line: 138 trace: { ./libraries/src/Factory.php:138 { Joomla\CMS\Factory::getApplication() › { › \tthrow new \Exception('Failed to start application', 500); › } } ./components/com_flexicontent/tasks/estorage.php:46 { …} ./components/com_flexicontent/tasks/estorage.php:23 { …} } }

When editing an article in backend, I also get this PHP error message:

Exception {#17 #message: "Failed to start application" #code: 500 #file: "/home/*********/public_html/libraries/src/Factory.php" #line: 138 trace: { /home/*********/public_html/libraries/src/Factory.php:138 { Joomla\CMS\Factory::getApplication() › { › \tthrow new \Exception('Failed to start application', 500); › } } /home/*********/public_html/components/com_flexicontent/tasks/estorage.php:46 { …} /home/*********/public_html/components/com_flexicontent/tasks/estorage.php:23 { …} } }

I have downloaded and instalkled latest Master zip from Github.
System info hereafter:

• PHP attivo su     Linux vps01 3.10.0-1160.45.1.el7.x86_64 #1 SMP Wed Oct 13 17:20:51 UTC 2021 x86_64
• Tipo database     mysql
• Versione database     10.1.48-MariaDB
• Collation database     latin1_swedish_ci
• Collation connessione database     utf8mb4_unicode_ci
• Crittografia connessione database     Nessuno
• Il server del database supporta la crittografia della connessione     No
• Versione PHP     7.4.25
• Web Server     Apache/2.4.6
• WebServer interfaccia PHP     cgi-fcgi
• Versione di Joomla!     Joomla! 4.0.4 Stable [ Furaha ] 24-October-2021 19:25 GMT
• User Agent     Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:94.0) Gecko/20100101 Firefox/94.0

                         
Can you pleaae help me to fix it?
Please feel fre to ask me more details if needed.

Thank you in advance

I forgot to mention I'm using custom templates (obviously coming from the j 3.10.3 site: they were working in old 3.x version.
I have tried to publish an article using standar FC article and it works on frontend.... some suggestions on adjusting my old custom templates?

Just a quick update to say how I solved this issue: I have found I was using a previos outdated version "default" template, no longer suitable in J4 FC version.
I had to switch to "grid" one, and then adjust my other custom templates/types cloning the grid one and making the adjustments I need to fit my own layout.
I hope this will help someone to don't waste time in looking somewere else to solve that kind of issue

hello migration template will be added in beta
for now doesn't use flexicontent to j4