I'm here to update that tempered glass DOES work on Mate 20 series. I bought a tempered glass from one of the Huawei stores here in the Philippines.
It cost 1k php ($20usd). Before placing the tempered glass they added some liquid on the screen. Then finish it off with a UV light to dry off the liquid under the tempered glass.
It took about 15-20 minutes process
It's been a week since I got it on and it still works. You have to press more firmly on the screen than usual but it does work. Accuracy drops a little though. Before with the regular plastic protector, it works at least 80% of the time. Now it drops to 60/70% or so.
Pressing it more firmly helps. Glad I took the plunge on the store. They promised me if it doesnt work, they'll refund me. Gladly it work.