While I don't know if this is specific to this years models, or if it's just the environment I was in - I was experiencing similar issues with my iPhone 11 Pro. My internet kept dropping, there was low connection, and I also kept getting several "incorrect password" messages when I was 1000% certain I was entering in the correct password. There are many intricate moving parts to connecting to Wifi, and again I'm not sure if there's anything different with the internal structure of the current line of iPhones or what but I didn't have any issues before.
If you're having issues with connection and having constant WiFi dropouts in your home when your previous model of your iPhones did not, I suggest looking into adjusting this setting on your router - it's called "DTIM Interval".
On some routers, the DTIM period can be adjusted.
Devices like laptops and iPads require high communication throughput and run on big batteries so on the DTIM scale, a DTIM period of "1" would suffice.
For cell phones, they require low communication throughput and run on smaller batteries - so a higher DTIM period is needed.
I'm not sure what it is about the 11 models but every model I had prior (Xs Max, X) didn't have any problem when my router was set to a DTIM period of 1.
My router is now set to a DTIM period of 3 and my dropped connections have virtually gone away.
https://routerguide.net/dtim-interval-period-best-setting/
Check your DTIM on your router and see if this even remotely helps! (may not but worth a shot, it worked for me.)