update: reinstalled openwrt, added pppoe details in /etc/config/network and enabled Software flow offloading. flowtable ft devices were updated to eth0.1, eth0.2 and pppoe-wan. I am getting the full connection speed now
Finally, today's snapshot seems to have worked well. for Lan Wan as well as the Wifi working well except one error which I can live with on LUCI
Switch switch0 has an unknown topology - the VLAN settings might not be accurate.
I am not touching it as the router finally worked and will not touch till I feel the need
You can ignore the warning "Switch switch0 has an unknown topology", LuCI is not adapted to such a configuration. However, it does not harm anything.
In https://github.com/namiltd/openwrt/tree/openwrt-23.05-rtl8367cd I created a version based on 23.05.4 for this router. You can test it.