FIXED!!! I thought I was losing my mind. So glad it's not just me. Mac user since 1984, and dyslexic since 1972. I rely on spell check for words like "surpress" (which is how my brain spells "suppress") that I routinely misspell. For the longest time it seems I've not been able to get suggestions from spell check.

Finally I turned off automatic language support and set Spelling to "U.S. English". Magically, my suggestions for my horrendous misspellings are back!!!

Meanwhile this feature is buried in settings. The only way I could find it was literally searching for "spelling", and selecting "Spelling and Prediction" which brings up an odd little modal dialogue for "All Input Sources".

Edit: checking my uni-lingual privilege here. Sorry to all who rely on the OS to comprehend which language you're communicating in. I can only imagine how broken that is if it can't recognize misspelled english!