Connectivity between a modern home router and an iPhone 7?

I wouldn't yet consider the iPhone 7 to be a 'legacy smart phone', especially seen as Apple is still continuing to push software updates for it.

In terms of capability, the iPhone 7, like most devices released before February of last year, uses Wi-Fi 5. The most recent revision is Wi-Fi 6 which is backwards compatible with Wi-Fi 5, so everything should just work!

The only issue that could occur is that, very rarely, if someone purposefully change the settings of the router, it may be misconfigured to only allow connections over Wi-Fi 6. To fix this you'll have to go into the router's settings and change it back.