Upgraded to new modem, but same slow wifi issues remain

This is simply the nature of Wi-Fi. You're unlikely to get close to gigabit speeds even with the best Wi-Fi access point and client sitting right next to each other. With multiple access points and multiple clients you can probably max out the gigabit connection, but it's not possible to test that from a single client. The speeds you're seeing are pretty much expected. (We might see slightly better speeds with Wi-Fi 6E if Industry Canada decides to open up the spectrum here for unlicensed access, but it'll be at least a few years before we see significant improvements beyond that.)

As for the boosters I think that's pretty much the expected speed from a Wi-Fi extender. If you want better than that you'll need to hard wire additional access points. I don't know if the boosters can do that as I've never used them. I also don't know if the boosters are capable of better speed wired in or if you'd need different access points.

As for the cameras you might want to reconfigure them, even if the Wi-Fi name and password haven't changed. I've found that some devices will need that done when swapping out the access point or router.