100%? Impossible. But they can effectively ban it.

Pass a law that makes any US company, or company doing business in the US, not allowed to host E2EE-enabled apps. This now bans them from the App Store and Play Store. 99% of users won't find or choose to side-load for android users. Then they can make E2EE actually illegal to distribute in the US. They'll almost never bother going after individuals, but this effectively makes hosting a US-based website unable to distribute E2EE programs. So people will need to use foreign sites. Which the US can force ISPs to block via a whack-a-mole on individual sites.

This isn't very likely, but hell Congress was decently close to banning TikTok for no real reason so who knows?

its like banning math

Tories are just trying to kick up as much shit as possible before they're kicked out so they can blame the next party for the fallout.