Me too. I've sideloaded hundreds so far. It's still working despite what others have said.hmm I must not be one of the affected, i’m sideloading practically any app i can think of just fine here with iMazing
However, I did see this note from an 11.3 beta tester, so be aware, there might be rocky roads ahead:
iMazing stopped working for me on the 11.3 beta, and apps that I’d previously installed using it don’t open.
I'd be very disappointed if this change is forced upon us in the public release of 11.3.