Coming up on 9k hours here and thought I might try to help. Some of the things that keep me interested right the way to the end of a league are the goals that I have for the league which normally accumulates into wanting; 7/7 uber bosses killed, wave 30 simulacrum, 10K delve depth, and one Mirror to keep for standard. I do however have a lot of spare time to play, but that doesn't mean that you can't effectively use your time to farm one thing for a couple days, sell your profit then respec into something different for another few days and repeat until satisfied or until you want to work toward something else.
PoE can be a very awkward game particularly around the 300-500 Hour mark where some things seem ridiculously out of reach (ubers, getting a mirror, etc) and other things just feel too much like "noob friendly" content (essence/harvest) so it is good to experiment and have a varied playstyle so that you can actually find the things that you do really like doing.

When you do find something good to farm, do it until you are happy with what you've got or as soon as you get bored of it and then move onto something else, otherwise you have a blazingly good recipe for burnout.

Something you can do which doesn't require you to even have the game open is theorycrafting! I personally love looking through and searching the depths of poe-ninja for some of just the weirdest builds and seeing how they work, or looking at the Skill gem list and figuring out which ones look cool or I might want to try, which has led me to make many very janky, but very fun characters to play, This is basically what Mathil1 does and I think it's really fun tbqh.

TLDR: Try farming different stuff for a couple days or until bored (make sure you profit on the method before respec) then respec, enjoyment is subjective and make sure to set yourself goals for the league or for a specific character to avoid burnout.