It really depends on what you are doing. If you are developing my first iOS app, then even with 8 GBs Xcode will run ok. You are unlikely to see many issues with 16 GBs. What you will appreciate is that even a base model MBA can open xcode and the simulator faster with a default project than a top of the range Intel Macbook pro. Even a base model will compile, build and run basic/medium complexity ios apps without breaking a sweat. I've seen a 16 GB MBA compiling Chromium faster than an i9 32 GB 16" Macbook Pro. It was something like 27 vs 32 minutes, iirc. if portability is not a requirement, then I would go for an M1 Mini, since it's the fastest in all developer tasks.
If you have tons of other apps going at the same time, like Outlook, a web browser, Word and Excel documents for references, Teams and Slack because that one team refuses to use Teams, then you will certainly appreciate having 16 GBs at least.