as chris said back camera can cause front to not work as well. try disconnecting the back camera and see if the front camera works (may or may not). also, what repair did you do? I’m assuming a screen replacement (most common repair on a phone after all). Check to make sure the prox/front camera flex cable didn’t receive any damage as well. Clean connectors for both front and back cameras. Power cycle device (disconnect battery and hold power button for 10-15 seconds to flush all power out of the board). If nothing else you can try to do a factory restore via itunes and see if there is a software glitch that caused the issue. That’s about all I can think of that may help restore functionality though beyond replacing the (most likely just the) rear camera, which for some reason is more expensive on the iphone 7 plus than any other iphone I’ve seen including xs max.
you may be able to splice the existing cable to a replacement. however the replacement would most likely need to be an OEM one from another broken device or such, and would require microsoldering equipment/experience. a replacement home button may not have touch id but it’ll still work fine as a home button
check first dirt/debris in the connectors. if everything is clean and no damage it may be a board issue. test with the original screen if you can and see if it happens. if original screen lcd was damaged/non functional then it may be safe to say it’s a board issue, though you could probably try 1 more screen just to be safe.
keep in mind if you insert an isesamo into the usual spot on the iphone 7/8 series, bottom left of screen, the home button flex cable is right there and is very easy to damage accidentally. I usually go in from bottom right on these particular devices.
test using voice memos. if you can record voice memos with no static sounding then the mics are okay and the fault likely lies with something in the network capabilities. maybe a new antennae but more likely board damage caused by the water
it will likely need an lcd assembly replacement. you can always try this yourself and source the parts, however it’s not something I’d necessarily recommend for a first repair attempt since it’s very easy to break the face id cable on the screen on these ones. if you go this route I’m sure there’s a guide on ifixit for it and I’d definitely follow it closely. otherwise you’ll want to try to find a reputable repair shop that can repair it for you and get a price quote
is this the original playstation 4 with the non-physical power button? if so you can remove the top cover (assuming you have the right tools) and put your finger on the gold sensor pad right underneath the button and see if it turns on. those devices were well known for having issues with the sensor power button not always working properly, which is why I think they reverted to a physical power button in the second model. if yours has a physical button and it clicks and still doesn’t turn on, it’s likely either a psu issue or something on the board. beyond trying with a known good psu, board level diagnostics/repairs aren’t DIY processes and can get pretty involved. that said it sounds like the psu may be good in your device.