Raspberry Pi router with Wireless

Hi Guys,
i am pretty new to networking in general but at work i have been assigned to prepare a RP4 that is supposed to function as a Router for our vlans and also as connection to a separate 'secondary 'Network that is supposed to provide our 'primary' network with an internet connection if needed.

The Raspberry has to connect to a WAP in the 'secondary' network using the wireless radio of the RP meaning that it has to forward the traffic from the wireless Interface to the ethernet port.
(Wireless AP in sec. Network => Raspberry WiFi Interface => Ethernet Attached Devices)
Seeing as i am not sure how I would do that, I would like to ask you guys for some support.

I have never before worked with OpenWrt or done anything major in a Linux environment, just want to give you a heads up. I will be thankful for whatever help i can get!

small network plan of how things are supposed to look in case clarification is needed!

Don't expect the performance to be particularly impressive if you're using Wifi on a Pi. But, this is a basic routed config where you will set the wireless as a client (sta mode) to the upstream wifi network, and that will be associated with a 'wwan' interface (often DHCP client protocol) which will be assigned to the wan firewall zone. From there, it should 'just work' for the wired lan connection... (as long as the upstream network is non-overlapping with the subnets of the downstream).

To create the VLANs on the pi, you'll create new network interfaces with device eth0.x where x is the VLAN ID. Associate those networks with the desired firewall zones and rules, and you should be set.