Font rendering problem wiht new illustator (the letters are unequal)

I have tried this.

I have also tried other variable fonts (Acumin variable concept), which show this effect a well, but not in that extent. It might be inherent to variable fonts, but might also be general problems of handling them in Adobe software.

I would ask  about this in type design forums. You could also try  https://community.adobe.com/t5/type-typography/bd-p/type-and-typography?page=1&sort=latest_replies&filter=all