There’s no magic with WiFi. It’s all radiative pattern, the gain on antennas. The Linksys didn’t put out a different kind of signal and your camera had to be able to respond.

If you have a brick wall that’s causing issues I normally don’t try to force a signal through it. I put an AP on the other side of it.

TP-Link AC1200 Wireless MU-MIMO Gigabit Indoor/Outdoor Access Point (EAP225-Outdoor) https://www.amazon.com/dp/B07953S2FD/

you can easily drill through the brick to pass an Ethernet cable through.

The solution to basically all WiFi problems is to put a wired AP there.

For the rest of your requirements: mesh is a poor solution if you’re looking for something long term. Mesh is made to be an easy fix, it’s bandaid solution for people who don’t want to make the investment. If you want something long term, start running Ethernet around your house. Put an AP in every room. Put an AP near where people conjugate (I put one next to every TV and hardwire each Tv; make sure toilets get coverage). With all the smart home devices you’re talking about you need more AP that are all using different channels. WiFi 6 is a lot about managing too many devices sharing the same channel. But if you are using enough channels then there shouldn’t be any congestion.

I am wondering if this might meet your needs. TP-Link Omada AC1200 Wireless Gigabit Outdoor Access Point | Business WiFi Solution w/ Mesh Support, Seamless Roaming & MU-MIMO | PoE Powered | SDN Integrated | Cloud Access & App (EAP225-Outdoor) https://www.amazon.com/dp/B07953S2FD/ref=cm_sw_r_apan_glc_fabc_D3BNCD144J3DMW8NTCB6