I have a site in Joomla 5.4.9 with Educon template.
I want to update Joomla to vs6, since Educon template (4.0.3) is compatible.
I updated template to 4.0.3, Helix to 3.1.4, SPPageBuilder 6.10.

All extensions are updated.
When I try to update Joomla, it says that I have to disable Behaviour – Backward Compatibility plugin, and make sure the site opens correctly.
But when I disable the plugin, and go to the site, it shows the message
"Sorry, there was a problem we could not recover from.
The server returned a "500 - Whoops, looks like something went wrong." "
PHP version is 8.3
Did I forget to update something before?
Can you help me solve it?