From what I’ve read and seen, Linux is the worst option if you’re concerned about battery life.

This is basically down to some hardware vendors writing crappy Linux drivers that don't include power saving features, while also not documenting the hardware so no one else can do it either. But that's only true of specific devices. For example, this is claimed to have 14 hours of battery life, on Linux:

https://system76.com/laptops/lemur

My x270 could pull about 20 hours on Linux when it was new (it did degrade a bit over time, as batteries do). I don't recall if I fiddled with any settings as this was five years ago and the laptop since died in an accident, but I don't think I did other than setting it to "power saving" instead of "balanced".

Before that I had a Dell XPS, which lasted about 7 hours IIRC, which was pretty good for the time.

My Acer could pull about 15 hours when new, but it is a fairly underwhelming Celeron CPU so that probably helps.

Maybe other systems are worse; I don't know, but overall things always seem to work well for me.

Try the starlabs starfighter.

Something without a second GPU. Linux never did quite get those working properly.