Apps targeting Android SDK 30 published by F-Droid cannot yet be installed on Android 11. This affects at least FairEmail, Netguard, OpenVPN and a few others.
You might want to hold up upgrading your device to Android 11 for a few weeks if you rely on any of these apps.
As a developer, you might want to hold up upgrading targetSDK to 30 for a bit.
The issue is tracked here, including a workaround for getting your data back from FairEmail in case you already fell into this trap.
▶ croservices: Cro 0.8.1 is here! Including a new Cro::WebApp distribution, which provides a templating engine, for those doing server-side web apps. Also, lots of other fixes and improvements. Enjoy! #perl6 https://cro.services/docs/releases#0.8.1
"Debian is back in the Mastodon/GNU Social fediverse, follow fosstodon.org/@debian" by Laura Arjona Reina https://larjona.wordpress.com/2018/12/21/debian-is-back-in-the-mastodon-gnu-social-fediverse-follow-fosstodon-org-debian/
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko