Able uppercases in username ?
Please note user registration and account creation is a part of WordPress core.
I'd suggest you try the solution mentioned in this support topic: https://wpforo.com/community/how-to-and-troubleshooting-2/registration-form-username/
In case you want to say thank you !)
We'd really appreciate and be thankful if you leave a good review on plugin page. This is the best way to say thank you to this project and support team.