I am seeing the same issue on my current Windows Server and a new Centos 8 server
Windows Server: Emby Server 220.127.116.11
New Centos 8 Server: Emby Server 18.104.22.168
Attaching Windows and Centos server logs
EDIT: Trying to open the Server Backup plugin but it seems to be affecting all the plugin selections
Yes this is affecting all plugin access via Plugins. If there is a Dashboard link you can still access. examples like Playback Reporting, Reports ect or via direct url.
You should be able to access the Server Configuration Backup via direct link if needed.
FYI you have a outdated PeopleBackup plugin installed "Info App: Loading PeopleBackup, Version=22.214.171.124". Current version is 126.96.36.199