I agree this is infuriating. This was the reason that made me finally ditch autocorrection altogether on my iPhone. I still make mistakes but at least now they're mostly my own mistakes, and when I correct them they stay corrected.
GP is saying he would like not to but cannot shut it off because they’re not using autocorrect but text replacements. It does make sense in the general case to sync text replacements, just not if you’re using it in place of autocorrect
Phase 1: iPhone w/o autocorrect but with text replacements.
Phase 2: iPhone and macOS, but text replacements are synched without option to disable. I don’t want autocorrect or replacements while typing on a real keyboard.
Phase 3 (reluctantly): iPhone with autocorrect, macOS without it, and no text replacements.
tl;dr it would be nice if I could disable text replacement on a per-device basis.
One solution is to disable autocorrect, then tap-type when you want no correction and swipe-type when you do (since swiping necessarily uses autocorrect)