Here is a utube video about it.
[FIXED] This browser or app may not be secure. Try using a different browser. If you’re already... - YouTube
copy and paste into google. it should come up (some of te comments might help also)

Here are some steps:
Use different browser
Turn on javascript in chrome
reinstall
use different computer

some comments
I HAVE A FIX go to your settings, click on privacy and security, click on security, then scroll down until you see "no protection", click on that, close chrome and try signing in again,

The only way I could fix it was to create a new profile

it worked after Turnoff the 2step verification

just sign out of every account on google and login to the one you wanna use

Hope this helps