“Include Anti Feature Apps” in Settings > App compatibility:

There you have to add the anti-features you may accept included in Apps. For OM you have to enable these:

(But not 100% sure about this. Maybe the first circled is also enough?)

You have to enable “Unwanted Features” in F-Droid settings before it shows up.

Link to the app: https://f-droid.org/packages/app.organicmaps/

Here you go:

https://www.bleepingcomputer.com/news/security/this-image-shows-its-own-md5-checksum-and-its-kind-of-a-big-deal/

(MD5 is not PGP, but impressive nonetheless)