My phone runs a desktop GNU/Linux OS with desktop Firefox (or Chromium if installed). If Firefox on desktop stops showing websites correctly, we will have a larger problem than an unsupported niche phone.
I expect that the real problem with using a Linux phone would be WhatsApp, Google Maps (the navigation part), OSMAnd. Telegram desktop maybe works.
If you’re downloading 200 mb pages every time because you’re loading desktop pages on your phone, it’ll be pretty slow and inefficient.
Also PWAs can use local storage.