Dear @lukass2000 ,

lukass2000 wrote

I would like to have a VLAN, which I only use for test purposes.

There should be no internet connection and no DHCP administration.

Each switch should be assigned a port that uses VLAN999.
So to speak, a virtual LAN cable is to be emulated.

For example, if I plug a NAS into switch 1 on the VLAN999 port, is to be accessed on switch 2 on the VLAN999 port via laptop, but without an automatic DHCP address assignment etc...

If you want no network access within the LAN, no DHCP server for each VLAN and static IPs for each device, then you just need to be careful to set only the VLANs and not the interfaces.
Note that each port connected to the switches is tagged with all VLANs (just set the VLAN, not the VLAN interface), and then set the port VLAN settings according to the client device.
You can refer to the following articles:

How to configure 802.1Q VLAN on TP-Link Easy Smart/Unmanaged Pro Switches?

How to configure 802.1Q VLAN on Smart and Managed switches using the new GUI?

Best Regards!

Dear @lukass2000 ，

But if i switch now a device to the Port with use VLAN111, than it is also listed in the "Clients List" from Omada Controller.
Is it correct that way?
Will the devices be listed even if the VLAN have Port Isolation?

Yes, it is correct. The clients will be still listed.

Best Regards!

Dear @lukass2000 ,

lukass2000 wrote
But the configuration as seen on the screenshots, is right, or?

Correct, but you can choose the port is Tagged or Untagged that you want.

Best Regards!