Folder pane broken after update

The folder pane is broken after upgrading from TB 91.7.0 to TB 91.8.0.

The folder pane is still broken after fresh installing TB 91.8.0.

More info
http://forums.mozillazine.org/viewtopic.php?f=39&t=3090555

There is a workaround in the thread. Maybe helpful to someone else.

Phoenity Icons 3.4
Thunderbird Portable 91.8.0 with 2 Google IMAP accounts
Windows 10 Pro 20H2 32-bit