If you mean “Can I access my Proton Mail accounts from Thunderbird”, yes. You need the bridge application from Proton to do it.

Thanks. Can I access all Protonmai accounts, both paid and free from TBird? Also can I access all Protonmai accounts, both paid and free, from all three devices?

Your questions are more about Proton Mail than Thunderbird.

The important thing is where the bridge application runs. Apparently, not on GrapheneOS: https://proton.me/support/operating-systems-supported-bridge

It seems that free accounts can be used only through webmail, not in clients such as Thunderbird: https://proton.me/support/proton-plans

Or just use Proton's apps on some or all platforms: https://proton.me/mail/download

I assume that the Android app runs on GrapheneOS.

Thanks. Can I access all Protonmai accounts, both paid and free from TBird? Also can I access all Protonmai accounts, both paid and free, from all three devices?

According to https://proton.me/mail/bridge :

"Proton Mail Bridge is available only with a paid plan that includes Proton Mail."