How do I fix Google account sign-in issue?

Can’t sign into my Google account anymore, I got to sign in and I put my username/Gmail address and when I go to hit next, it takes half the Gmail address away and the words email or phone number show back up and it won’t let me sign in. This just started happening a month ago or so maybe, any ideas how to fix it i’ve tried searching for the answer, but you get 100 answers of anything but what I need?

[Re-Titled by Moderator]