I encoutered somewhat of the same issue, only difference was that it was an existing client. After updating both server (latest v18) and the client. The client couldn’t connect anymore.
changing the config Cannot grant access
resulted in a working grant access in the browser.
removing account in the client, and removing all client settings, then readding the account worked. After this, I was able to get the client syncing again.
Generate App password doesn’t help in this particular case.
Oh, this is a windows client only issue, not seeing this on any of the linux desktops