"buildContainer() must be of the type int, string given..." on adding content

[rupasix]

Typo3 10.4.5
I check the latest version from github. I get this error when adding content to a column:

edit: Propably it's important - EXT:mask is installed on that T3 instance.

[rupasix]

I removed EXT:mask, it is not his fault, the error remains.