I wouldn't use F-Droid exclusively. Many apps can simply be downloaded from their respective webpages. GrapheneOS also has also its own very basic app store.

FDroid offers the guarantee that the apk was built from source, and at least some marginal safety in terms of having passed their security and analytics/ads checkers.

You lose all that if you go directly to source.

Obtainium makes it easy to download apps directly from their webpages. Many of them have ready configurations you can simply add: https://apps.obtainium.imranr.dev/