I finish the main quest first before doing everything else.

I've never finished the main questline. I always play for many hours doing other stuff, then get bored with my character build and start over with something else.

Regarding Blackreach (this includes spoilers):

I have never figured out what to do with Dravins Bow underneath the thieves guild.

Skyrim was my first Elder Scrolls game. During my first play through I climbed High Hrothgar the hard way. Once I reached the top, found out there's actually a nice road on the other side of the mountain lol.

Every playthrough I do, I install new lands mods like Bruma, as well as a bunch of follower mods, all of which I never wind up even going to or meeting cuz I tend to stick with some of the simpler followers such as those in 3DNPC or something like that, and can't figure out how to work it into the roleplay that I go to the new lands

I have also never beat the Thieves Guild or Dark Brotherhood questlines even though I have had the game for over 9 years

I can't stay engaged with long quests.

I have always had so many mods that I don't really know what is original and not anymore(to some extent). It was too many years ago I played without.

I have never finished the main quest or any of the bigger side quest like siding with imperials or storm cloaks. I finished dark brooder hood multiple times and companions once and almost did the thieves guild (I was so close, then I got bored). I actually finished one dlc (dragonborn) but that is all. Most of my gameplay is exploring caves and dwemer civilizations and random small quests that was in my direction like killing bandits or giving ingredients/items.