Well of course you need a computer to run the IDE. Xcode only runs on Macs. It is possible to develop and sign code without Xcode if you have access to a different sort of computer, but that is a level of masochism unrelated to productivity. (As opposed to Xcode which is a level of masochism related to productivity.)

Macs have a long shelf life, and ones capable of running current Xcode are thrown to the recycler, I assume you could nab one for minimal coin too. They'll be slower, like 1/3 the speed to build compared to new machines, but apps don't take long to build. Most of your time is "sitting and staring" followed by "typing". Neither of which is appreciably impacted by using an old machine.

I went from an 8 year old Mini to a new M1 when they came out. A world of difference! Buttery smooth window drags, gorgeous scrolling. But I don't really program apps any faster. Sure, I have a few seconds now and then on a build, but it doesn't add up to much. Then I switched up to a Studio with a brain the size of a planet… no real change for app programming.

Don't let lack of a computer be a problem. Grab an old mini and do your thing.