Sweatcoin does now track indoor steps, including treadmills, elliptical trainers, stepmills etc. Unfortunately, you do have to have iPhone 7 or newer, Apple Watch 2 or newer mobile, I know Android mobiles are supported but not too sure on the minimum specifications. I’m sure another user will fill in the blanks for the Android world fairly quickly. Or of course there other a few other threads discussing Android and indoor steps which could help.
As far as I’m aware I’m on the Apple Watch 2 and above are the only smart watches supported at present.
I appreciate that you made the point clearly that you don’t normally run with the phone but unfortunately they’re still has to be a way to count the moment whether it be a belt, harness or pocket with a mobile phone or Apple Watch.
There are also a few threads discussing how people carry or wear their phones that works well, or not so well for them which may also prove useful.