OpenWrt - can't connect two subnets

Hi guys,
I'm in desperate need of assistance to somehow organize my home network: Long story short: I've bought Tenda Nova mesh which has very poor configuration capabilities -I was able to get it working in bridge mode, but it's lacking the "Guest Wifi" which I need for my family to separate them from my devices like TV or Printers(Tenda does not offer Multiple SSID).

To get any type of "configuration" I have to switch the Mesh to DHCP Mode which automatically creates a new subnet for wireless devices under IP:| Mask
My LAN, so OpenWrt Router is on IP.| Mask
Currently, the status is looking like this:
Devices on subnet 192.168.9.x are able to connect to Plex or OpenWRT router (so 192.168.9.x -> 192.168.0.x is working), but my PC is not able to locate my wireless printer, TV etc which is on 192.168.9.x (so 192.168.0.x -> 192.168.9.x not working). Tenda won't even allow me to change the default mask to something else than
Can I somehow configure the OpenWRT router so devices under could see and connect to I was trying to use the Route Static option with Destination and mask but it didn't work.

Below is a simple diagram of the setup:


This is not a problem with Openwrt, or the configuration on your Openwrt board. This is the firewall of the Tenda blocking the incoming connections. Do whatever you can to disable the firewall on the Tenda Mesh completely. It's not needed as the Openwrt board is handling WAN firewall between you and the internet.