first off, there is no spyware shipped with iOS, iOS is the spyware. aside from apple being repeatedly caught lying about the extent of its spying, the convoluted and cumbersome iCloud decoupling with the unencrypted backups and the fact that you have a covert peer-to-peer network running on your own hardware that you can’t turn off or opt out of should be more than enough to give those fucks zero benefit of doubt.
second, if you’ve been on iOS since the iPhone X days, you have no idea what’s possible on this side of the fence. that’s why I’m suggesting getting a cheap, yet capable, used phone and figuring out things without breaking the budget. you could get a flagship pixel or whatnot for the same purpose, but this is the beauty of android - a $50 phone runs the same software as a $1000 one.
I assure you, you’re plenty safe and secure with a regular, supported lineageOS build, unless you’re pursued by nation-state actors and such. the postmarketOS and friends note was to illustrate the plethora of options you got with the same piece of hardware; none of them are ready for prime time.
it also has the OPDS plugin, so compatible Android readers can get books directly off it