hopefully I found the right title for my problem. Having the latest RouterOS and read through a lot of articles and tried for hours I can't get done what I want. I found the wiki articles talking about the switch chip type for the hEX, the new VLAN filtering approach since 6.41, but still...
Right now I have two networks:
Net1: 192.168.55.0/24 having a DCHP Server
Net2: 192.168.66.0/24 having a DCHP Server
Net1 connected to ether1, Net1 available as vlan10 at ether 5 (VLAN trunk)
Net2 connected to ether2, Net2 available as vlan20 at ether 5 (VLAN trunk)
In addition setup two vlans (vlan30 and vlan40 with DHCP Servers) on the hEX available at ether 5 (VLAN trunk)
Block vlan30 against vlan40 and vice versa (Should be easy with a firewall rule)
ether 5 (VLAN trunk) will be connected to a managed switch in another building (I only have a single network cable going there).
As said, I failed in setting up this scenario. Maybe my approach is too weird. I'm grateful for any help.