I had exactly the same problem tried https://dev.azure.com on Edge , Chrome and newly installed Firefox and was redirected to the Get started with Azure page with no option to log into Azure Dev Ops.
What solved the problem for me was requesting https://dev.azure.com/myidentifier
where myidentifier might be a name and a 4 digit number or whatever identifier Azure Dev Ops uses to identify your account, hopefully you’ll have a note of this identifier !
This is not an ideal solution though. Ideally Microsoft should allow a direct log in from dev.azure.com.