Pablo's patch also worked for us.
Gracias por compartir,
m.
DON'T APPLY FORMER WORKAROUND...
I learned the hard way... I've been recovering my site from the backup for a few hours now.
The error goes away but then new problems arise and the site becomes unusable.
I suspect that, as discussed in this other issue, the problem is that we have done a partial manual upgrade and the plugin versions are no longer the correct ones:
https://www.drupal.org/project/varbase/issues/3242627 →
Perhaps the best option is to revert the bootstrap_layout_builder plugin to version 2.0.1 as suggested by Aastrong?
Anybody can confirm the temporary solution?
Same issue here.
This issue looks related:
https://www.drupal.org/project/bootstrap_layout_builder/issues/3157754 →
Rolling back to 2.0.1 till this is fixed.