Hopefully not otherwise these IPAs would be pirated and injected with a mother truck load of malware and spyware.
Not true.
Installing original IPA (which belongs to your AppleID) - is never a problem and in this context sideloading on M1 means exactly that. It works.
Older iTunes were also backing up IPAs this way.
This is useful if you want to keep older version of the app - which is original and belongs to your AppleID.
iOS (and MacOS) check for 2 things on IPA:
- the valid Apple Developer Certificate (renewed yearly)
- your AppleID signature of the IPA (proof of ownership)
Where piracy/malware are at play?
iOS
can accept sideloading of non-Appstore IPAs (pirated or with malware - or both) without jailbreaking.
Most of (illegal) 3rd party Appstores are "providing" these modified IPAs.
If they provide them for free - apps will work but will require reinstall after 7 days, as they are signed with free AppleID.
If you are required to pay subscription - apps will work without time limit (as sellers use the money is used to fund Apple Developer Certificate)
However Apple tracks down these misused Developer Certificates - and you may be required again to reinstall the app. Plus your "subscription" is out of your hands - at mercy of Apple towards that "fallen" developer.
Pointless, its better to pay on Apple Store once and have the app forever.
Second - indeed - malware is a risk.