Safari cannot access the internet, but apps and other browser can

My dad is having a very strange issue with his iPhone. He has the iPhone XR and for the last couple of weeks or so, he has suddenly started having a very strange issue that we absolutely cannot get to the bottom of. All of his apps (i.e. Facebook, Facebook messenger, his Gmail app, etc.) can access the internet with no problems whatsoever; however, whenever he tries to open an external link from any of those apps or even if he just opens Safari to try to go to a website, it says, "Safari cannot open this page because your phone is not connected to the internet." His phone absolutely IS connected to the internet. He ONLY get this error when he's on LTE and not connected to wi-fi. The wi-fi in my parents' house is a bit spotty because their house is quite large, so my parents just use T-Mobile's LTE since it's much faster. We have tried everything we can think of to try and fix this, including resetting his iPhone and resetting his network settings to no avail. Last night, we had him install Google Chrome on his phone to see if he could access the internet using that browser on LTE and that works perfectly fine and loads websites with no issues at all. So, we figured an easy solution to this problem would be to totally bypass Safari and just have him set Google Chrome as his default browser since this issue is clearly isolated to Safari itself. However, even after doing this, all of his apps STILL try open Safari whenever he tries to open any links from his email, Facebook, etc., and he gets this error about his phone not being connected to the internet, even though he now has Google Chrome set as his default browser. We are all at a total loss. Does anyone have any ideas as to what could be causing this and how to fix it? We have tried EVERYTHING.

Thanks in advance.