Error with T4_bs5_blank on Joomla 4.2.1

I have a problem with the T4_bs5_blank template and Joomla 4.2.1.
When I update my site tot Joomla 4.2.1 I get this error:

count(): Argument #1 ($value) must be of type Countable|array, null given

Only when I put the website off-line and logon on the frontend with my superuser account, the error does not appear.

For the moment, I still can use an older version of Joomla, but I will miss the security updates.

I disabled the login module and replaced it with a Login menu item in main menu. That seems to work.

I tried to update to the latest version of Joomla but could not replicate the same issue. If the problem still persists in J!4.2.2, pls let us know.

I solved it by temporarily downgrading php from 8 to 7.4.30

Let me know if you need further assistance.