Dear Milan, this is not an Astroid or template bug. 
I have now tested this extensively and set up a new Joomla 4.3.3 and Joomla 5.0.3 installation. Both are running PHP 8.3.3 and Maria DB. Then I first installed Astroid 3.0.11 and the Classic Template 1.3.17. Everything is wonderful. 

The update to Astroid 3.0.12 was then displayed and installed. 
Result: no errors and everything works. 
Therefore I assume that an extension or plugin in your Joomla version is the cause. 

Which PHP version and DB are you using?

Unfortunately, we cannot afford to investigate your individual problem now within our support framework. 
That goes in the direction of individual support. 

I hope you understand that.

It continues here:
github.com/templaza/astroid-framework/issues/620

Thes are my versions:
PHP Version 8.2.16
10.6.16-MariaDB

Regards,
Milian

Maybe we will wait fo a solution at github.

These are the bugs.
hope there is a solution...

Same error on B2B template - just discovered today.
Looking forward to solution!

Gina G.
GAWD Productions

Where exactly after which action does this error appear in the backend? 
You have to describe this to us in more detail because this doesn't happen with us!