I had this issue, and following the instructions at https://thesleepyadmins.com/2024/01/26/windows-server-2022-rds-ha-broker-privilege-not-held/ resolved it for me.
The short version: On the second server, delete the Registry value HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tssdis\Parameters\DBConnString; remove the RDS server roles; and reboot.