Help (Pixel) spell check not working, autocorrect disabled but still replacing

Spell check often doesn't work in Keep Notes; no red lines appear under misspelled words, even after restarting the phone. The following are enabled:

Gboard > Text correction > Spell check

System > Languages & input > Spell checker

Also, it seems words are sometimes autoreplaced although the following are disabled, and I'm pretty sure I didn't accidentally tap the suggestion strip while typing:

Gboard > Text correction > Auto-correction


Spacecorp test pilot
I don't know about Keep Notes as I don't use that, but actual text correction is purely a keyboard feature. I've not use GBoard lately, but I've no memory of it correcting when I didn't tell it to, and I don't know how easy it is to rule out that you may have accidentally touched the suggestion bar if it only happens occasionally. But if the settings are as you want them and you aren't happy with the behaviour then as others have said the answer is to try a different keyboard app - just remember that as a different app will have slightly different key spacings (though some let you customise that) your muscle memory will need a little time to adjust.