Please share a screenshot so we can see what you mean.
Also find the nextcloud.log file in the sub-directories of /var/www and see if it has any errors.
Pre update the background of the βLook at meβ Login Note was the same colour as the background of the Log in button, ie. it was the Theming β Color setting. This is a test system, but also doing it on our production too. Notice the Markup is not impacted.
I am not seeing any 404/500 errors in the apache access or error logs. The nextcloud log is not capturing any issues as I load the page.
We are using the tidy URLs code in the .htaccess file, but disabling that does NOT fix the issue.