Hi, thanks for report. This is new to me. I did not notice any specific changes to sdcard on android 8.1. I dont have device with android 8.1, but i can test it in emulator. I now worked a lot on storages support from android 11 and version is not yet out. But this is different.
Do you mean to have data on sdcard on public location or in /android/data/bruenor.magicbox ?
Hm, but wait, there is no way how magic dosbox can save state on sdcard? Only new (still unreleased) version can do it. With save state you mean “Save State” from general settings menu, or the way how game saves self?