One backup job stays in queued state for about 2,5hours then continues.
The client is connected via a VPN (wireguard). To be honest, the network speed is poor(~40-50 Mbit/s)
How can I imporve this? Maybe it is caused by an antivirus system (sentinel)
It could be the anti-virus holding on to the volume. Turn it off then test.BE is not designed for remote backups, so expect poor performance, especially when a VPN is involved.