Template corrupts when php version updated

I,m having a serious issue with the adventure template I'm using for a new website. Twice I have tried to upgrade the php version to php8 from php7.4 and each time the site gets corrupted and I am unable to access the administrator or view the front end. With the current attempt to change the php version the website is still unaccessible. My hosting provider suggested I speak with the developer. I dont know how to proceed with this and I dont understand why the php version wont work and cant be restored back to the working version.

I have attached a screenshot of the error page that appears when I try to log into the admin.
Has anyone encountered this issue?

Regards,
John

Hello,
more information pls.
1.) Template version
2.) Astroid version
3.) Exact PHP version
...
Usually there is no problem during php update.
Anyway, please disable all cache tools, Joomla cache and php chache.

Ive managed to get the website back up but only with the lower php version.

The template is Adventure
The current php version that is working is PHP 7.4.30
The joomla version is 4.2.8
The template version is 1.3.11

Twice Ive tried to upgrade the php to version 8.0 and had the same result as shown in previous attachment.

Regards,
John

The Astroid Framework is:
Framework Version: 2.6.3
Template Version: 1.3.11

Regards,
John

First update to:
Framework Version: 2.6.4
Template Version: 1.3.12
Joomla 4.2.9