Google recommends to split your AAB export to Google Play into separate 32 & 64-bit App Bundles to optimise download size. This is also stated in the Godot documentation. But when doing this and uploading to Google Play, you get following error on the 64-bit version:
Error: Usage of 64-bit native libraries is disabled, but App Bundle contains only 64-bit native libraries. This usually happens if you have included 32 bit RenderScript files (.bc), but only have 64-bit native code.
I have found a solution for this, so I will answer my own question. Posting here in case someone else hits the same problem. Surely I can't be the only one who's had this?