Hard habit to break. I learned it so long ago too.
Haha I learned to type organically, and it was only in my mid-40s that I retrained myself to type the correct way. It took something like 40 hours of practice on keybr.com before I could get close enough to my regular typing speed, such that I could switch over to the 'correct' method without it impacting my work.
Retraining myself to stop doing double-spaces took maybe a week.
You can tell when I've edited something on both a phone and a physical keyboard, based on the inconsistent use of spaces.