It sounds like you are confusing open source with copyleft.
Copyleft is a great thing, but it's also fine for things to be open source and not copyleft.
I can use syncthing because of Mobius. If Mobius did not exist, I would either have to pay a bounty to get someone to port Syncthing or use something else. That bounty is more than $6.
You can still port syncthing yourself. Mobius is not stopping you! You'll have to pay Apple $99 a year, and you will have to handle the app store process, and all - but you can do it. Neither syncthing nor Mobius will stop you.
Joining the Apple developer program requires that you dox yourself to Apple, and ties that government identity to device hardware serial numbers. I buy my Apple devices for cash and use each one with a unique disposable Apple ID created with a burner email address and burner prepaid phone number.
This is also one of the reasons I can't pay for IAP cancer - attaching payment methods links identity to the Apple ID and hardware serial number.
Copyleft is a great thing, but it's also fine for things to be open source and not copyleft.
I can use syncthing because of Mobius. If Mobius did not exist, I would either have to pay a bounty to get someone to port Syncthing or use something else. That bounty is more than $6.
You can still port syncthing yourself. Mobius is not stopping you! You'll have to pay Apple $99 a year, and you will have to handle the app store process, and all - but you can do it. Neither syncthing nor Mobius will stop you.