Also you may try move the main router away and link up tplink router to the modem directly. It seems that you have double-NAT on both sites. IPSec can only work for tplink router's LAN. It won't help...

@Phil.S.K. I don't think you need to enable Open VPN. IPSec is good enough. The issue seems like subnet problem, you may check the settings if you have 255.255.255.0 correctly. The controller has...

@atj15 ER7206 can handle 300-500 client devices. ER605 can only handle 50-75. When you calculate the client number, IoT devices can be ignored, because they do not use heavy traffic

@Harry_T You may check Duplex Mode of the LAN ports of the router. On router web interface Network-->Switching-->Port Status. Try change negotiation mode to 100M Full-duplex

@wondering That's right, you will need to modify the router IP in standalone mode first. Here is an instruction

@Maverick88 1008H NVR can only detect ONVIF compatible cameras. You may check if Tapo cameras support ONVIF