In the coming 20H1 update, MS have identified severe performance issues for WMR users of SteamVR and advise that such users do not update until the fix is released ( expected shortly after the general release )
Source: https://www.reddit.com/r/WindowsMR/comments/g36az0/clarifying_windows_mixed_reality_issues_on/
Source: https://www.reddit.com/r/WindowsMR/comments/g36az0/clarifying_windows_mixed_reality_issues_on/