Balancing two different network over Wlan or lan

This is my current network topology.

I would like to make the bandwidth on my 1st Connection (Fibre) available on my OpenWrt router that dials a 2nd connection (PPPoE via Eth) and the connected Dumb wifi6 Ap.
Both are same ISP and same plans, but different public ipv4/v6.
I know that to achieve double bandwidth is not possible but would like to know about load balancing and weather it would work for 2 clients connected to my Wifi6 AP ; I.e; if 2 clients connected to my wifi6 AP be able to get 120Mbps each simultaneously?


This is pretty much the same question

Yes I see it didn't work well for op.
I wanted to ask if I can connect the 2 routers using 5ghz wifi, is it possible to merge both wan then?

Edit: Got the setup to work and am getting pretty much twice speed on Speedtest.
But when trying to use upnp(libretorrent) it loads the CPU upto values >2 and system stutters. Anything I can do about this? Also the Active Connections bar rapidly fills to 99%.
Any help would be appreciated.