I was recommended by those at firebase to post here, given that the bug I'm facing may be due to Xcode/SPM. I'll link the issue here but in short, I'm using firebase in SPM, and when I archive my app (10K lines of code, not a giant app by any means) for MacCatalyst, I face no issues. When I select archive for 'Any iOS device (arm64)' I get the error
scattered reloc r_address too large for architecture armv7.
I'm using Xcode 12.3 on an M1 MacBook Air, but I've tried archiving the same project on Xcode 12.2 and on an Intel MacBook Pro but the same issue arose.