I ran into the same problem and ended up switching to an S3 with Vultr. It’s been a while since I did it but here are the links that I used to figure it out. I’m deployed using Lemmy-Easy-Deploy.
I used a combination of:
https://lemmy.world/post/538280
https://github.com/ubergeek77/Lemmy-Easy-Deploy/blob/main/ADVANCED_CONFIGURATION.md
https://git.asonix.dog/asonix/pict-rs/#user-content-filesystem-to-object-storage-migration
Good luck!
This is the one I use to host on a vps. No clue on it’s deployability on a pi.
https://github.com/ubergeek77/Lemmy-Easy-Deploy
It’s auto installs and updates. Just need to forward the DNS for your instance to whatever domain name you like. It’s pretty straight forward from the documentation.