Correct. If I remove the save then the ROM will take me to the tutorial and everything. I hadn’t done an md5 check but your first question had me try something else: i removed the save, started a new game on my phone and saved it the first moment I could. Closed retroarch and restarted it on my phone again, and I got the error again, even though the sage was created by that exact retroarch instance. Then i tried the mew save on the deck and it loaded fine. Seems like I just have an issue with retro arch on my other devices but not the save itself.
Install flatpak and/or distrobox and you have everything you need.