I've been happily using "GNU/Linux phones" since 2008, with only 2-3 years around 2017 of using an Android device as a backup, so there's no need to "hope"; you can just act.
From 2008 to about 2011: Neo Freerunner, first on Om2007.2, then on SHR.
Then Nokia N900 with Maemo 5, in 2017-2019 augmented by Samsung Galaxy S3 with LineageOS as a secondary device since N900 was getting unusable for the Web by then.
And finally since 2020 up to now, Librem 5 with PureOS, which removed the need to carry an Android device again.
If so, I might be able invert my plan: use the Linux phone with phone/5G/useful software most of the time, and a cheap android phone in my bag that only comes out for things that need the monopoly apps and tethers to the useful one occasionally when necessary.
Depends on your definition of "lasting an entire day", but for me it lasts just long enough to usually not bother carrying a power bank with me. Usage patterns vary though.