Aspect ratio (full screen display) of old apps

I’m using some old apps (eBook reader and text editor) which don’t fill the entire display: they leave an unused empty space at the bottom of the display.

Lineage did introduce a fix some time ago which is supposed to address this issue. There is a related setting for “full screen apps” in the display settings of /e/OS.

Unfortunately the fix never seemed to work on /e/OS: old apps are displayed without aspect ratio adjustment and the “full screen” app selection setting doesn’t show anything (and crashes on repeated execution). This didn’t work in A14 and also fails in the latest release (3.2 A15 for Moto G32).

Is this feature supposed to work? Any (adb) option to debug the cause on my device?