I think it needs a signond oauth2 plugin to work. However, it is propably not packaged yet as there’s an open package request for it here: Package request: signon-plugin-oauth2 · Issue #263299 · NixOS/nixpkgs · GitHub
You can check if it is the same issue, by first following journal:
$ journalctl --user --follow
And then attempt to add the google account, which should show something like this in the journal output:
heinä 23 20:17:44 dellxps13 systemsettings[355746]: "google"
heinä 23 20:17:44 dellxps13 systemsettings[355746]: Looking for plugin ""
heinä 23 20:17:44 dellxps13 systemsettings[355746]: Starting auth session with "oauth2"
heinä 23 20:17:44 dellxps13 signonpluginprocess[355819]: "Failed to load /nix/store/9hkg33k08i33v5cjsbn9xlq2hsl2l10p-signond-8.61-unstable-2023-11-24/lib/signon/liboauth2plugin.so (reason: Cannot load library /nix/store/9hkg33k08i33v5cjsbn9xlq2hsl2l10p-signond-8.61-unstable-2023-11-24/lib/signon/liboauth2plugin.so: /nix/store/9hkg33k08i33v5cjsbn9xlq2hsl2l10p-signond-8.61-unstable-2023-11-24/lib/signon/haswell/libliboauth2plugin.so: cannot open shared object file: No such file or directory)"
heinä 23 20:17:44 dellxps13 systemsettings[355746]: Error:
heinä 23 20:17:44 dellxps13 systemsettings[355746]: "Authentication method is not known."