Here is the proper format that should work for you
$MfaClaimRule = 'c:[Type == "https://schemas.microsoft.com/ws/2008/06/identity/claims/groupsid", Value == "S-1-5-21-2526025855-2090947552-105674"] => issue(Type = "https://schemas.microsoft.com/ws/2008/06/identity/claims/authenticationmethod", Value = "https://schemas.microsoft.com/claims/multipleauthn");'
Set-AdfsAdditionalAuthenticationRule $MfaClaimRule