I always just save the boarding pass PDF to Dropbox on my phone because I don't want to bother downloading the shitty app for every single airline (plus who knows just what personal data they are scraping from my phone). Never had a problem for ~hundreds of flights with ~dozens of European airlines over the last three years. This includes Ryanair and the other hyper-budget airlines that seem to use flights as a loss leader for their lucrative "extra-charges" business.
It's also possible to import the boarding pass into Google Pay. The "correct" way to do it is through the airline's app, but I couldn't for the life of me get the EasyJet app to do it, and I really don't want to keep a number of budget airline shitty apps installed anyway, so I googled a bit and found
https://play.google.com/store/apps/details?id=color.dev.com...., which allowed me to scan the barcode from the PDF boarding pass and import that into Google Pay. Tested it with EasyJet only so far, will try RyanAir later. It's possible to tweak the boarding pass a bit, even change the barcode to QR code, but I haven't tried that and it doesn't seem to be necessary.
I think the whole "you must print the PDF boarding pass" thing is just about saving time. Imagine an older person in a hurry trying to zoom the PDF just right and also max the brightness. My wife (30-ish) struggles to do this without slowing down the queue.
