Yes, Session is available on F-Droid. Please note that you won't be able to navigate to the official Session repo by just searching for Session on F-Droid. Instead, follow the steps below:
Add via link
To install Session via F-Droid, you will first need to install the F-Droid app. Then, visit this link on any Android device to add the official Session repo to your F-Droid app. You can then proceed to install Session from F-Droid.
Add manually
To manually add Session to your F-Droid app, you will need the below repository address and fingerprint.
Repository address:https://fdroid.getsession.org/fdroid/repo
Fingerprint:DB0E5297EB65CC22D6BD93C869943BDCFCB6A07DC69A48A0DD8C7BA698EC04E6
Follow these steps:
1. Open the F-Droid app.
2. Open the F-Droid Settings menu.
3. Select "Repository".
4. Hit the plus (+) button to add a new repository.
5. Copy and paste the Session repository link found above.
6. Enter the fingerprint found above.
7. Session's official repository should now be added to your F-Droid app. You can then proceed to install Session from F-Droid.