> you must install an app on your phone
I _love_ those. When I'm trying to configure my modem, nothing gets my nether regions tingly faster than
(1) Visiting the documented configuration site on the back of the modem
(2) It 404s in a new and excitingly different way from every other modem you've owned
(3) After visiting a nearby business with working internet, the helpful interblags populace suggests you need an app, for ... reasons
(3a) At least in the old days, that was just a blatant money grab (harvest your location history and contact list, spam notifications, and so on). Now with halfway decent permissions it's less clear why they're such a-holes about it.
(4) You have the foresight to install the app while internet is available.
(5) Your phone is 2 years old, and the manufacturer views bare-minimum due-diligence updates as a liability and hasn't packaged the latest OS updates. Google simultaneously doesn't trust you to update your phone without somebody-other-than-them taking the liability and also highly recommends all their app developers to only target the very latest Android version. None of the modem-makeitbetter-thingamawhutts work on your phone because 2yo devices are practically fossil fuels in the making at this point.
(6) You surf the interblags for an old version of the modem-makeitbetter-thingamawhutts. After searching long enough, you have a >50% chance of having found the real archive and not a virus, since Google refuses to host old APKs.
(7) By sheer luck, that suffices, and your modem manufacturer doesn't have one of those "your thingamawhutt version is too old" screens in their app.
(8) You go back home, where it's safe and all is well, and when you try to configure your modem you find that the app only works if it can phone home to the mothership. That's a fine thing to want to do, except the only reason you're using the blasted app is because you don't have internet at home and would like to rectify the deficiency.
(9) After a bit of contemplation on the life choices that led you to this moment, you recall that your wife's phone can produce a hotspot that might remedy the immediate clusterfuck.
(10) That doesn't work. Her phone has internet and working hardware, but Google has decided to ask her cell provider if she's allowed to share the hardware she purchased with nearby devices for a single crisis moment. Her cell provider says that she can do anything she would like with the device she paid for and owns, so long as they also get paid repeatedly.
And so on. I'm having fun, reply if you want me to continue the saga, but IME an app is a very poor choice for configuring a modem, and that sort of bullshit has bit me in more ways than I can count. Even when you can get the damned thing to work, like OP mentions, the settings aren't anywhere near as nice as what the firmware natively supports.