I think you can set it up to get pull notifications (like every 15 or 30 min), a...

ptidhomme on April 22, 2022 | parent | context | favorite | on: K-9 Mail 6.000

I think you can set it up to get pull notifications (like every 15 or 30 min), and then disable "battery optimisation" for the app (that is, set it to "no restriction"). In my experience (my wife's GrapheneOS phone) it doesn't drain that much battery anyway.