Clients using protocol version 3.3 can't connect to RealVNC server version 7.12.1 (latest), at least on Raspberry PI OS Bookworm 64-bit

I have Raspberry PI OS Bookworm 64-bit (with X11 backend).

I installed the latest (version 7.12.1) RealVNC server from the RealVNC server download page and left the settings intact. (I also tried realvnc-vnc-server from the repositiory with the same effect.)

No matter which Authentication (VNC password, Unix password, None) I set in server settings, 3rd party and even RealVNC own clients using protocol version 3.3 can not connect to the server with the following message: "No configured security type is supported by 3.3 VNC Viewer".

RealVNC viewer for macOS can not connect, if I limit the protocol version to 3.3 in it.

RealVNC viewer for Android has no protocol version setting, but if I limit the protocol version to 3.3 at the server, the viewer can't connect with the same error message.

I have also tried other 3rd party RealVNC clients and Authentication combinations.

P. S. Other VNC servers, like x11vnc, work normally on the same Raspberry machine.