both are solid options, lineageos is just android while sailfish is a whole different os and doesn't work natively with android apps

Try both and report back.

I've only used SailfishOS and the hardware experience on the Sony Xperia 10 III was good. I think everything worked.

First of all: i havent used sailfish nor a Sony 10 IV so take everything with a grain of salt, but:

When looking for a familiar alternative to normal android, lineage is your go to. If there is an official build for the device it will most certainly work for everything in its power.

If a banking app doesn't allow running without google services, it won't run on degoogled lineage, but that's not really lineages fault.

I used lineage for years, and though you sometimes "feel" its a custom ROM (sometimes something doesn't work on the first try but randomly on the third, and the like) I always was able to satisfy my needs in a phone.

If you rely on apps that purposely don't run on custom ROMs, and can't find an alternative, you will need a second drawer smartphone for those I fear, but I don't think this would be any better under sailfish.

LineageOS is android and more secure because of that. Android has strict selinux policy's and good sandboxing i would not use a linux phone.

Salfish will be nore fun but guve you more headaches, lineage will be less fun buy give you less

I don't know what the state of either is on a Sony 10 IV, but the answer is almost certainly Lineage. It's the more mature project, and it's way more likely to work. And at the risk of getting on a high horse, Lineage's unfortunate but necessary (if you actually want your phone to work) reliance on proprietary blobs is already bad enough; I certainly wouldn't trust my privacy to a project like Sailfish, which I understand to be partially closed source.