Greetings Adam, and welcome to the twinking scene.
Unfortunately only a few pieces of gear from wotlk Era content is still considered BIS. Given the recent Stat squish that occurred in the BFA prepatch, your typical full ICC25H tier is no longer BIS (you will be delighted to know set effects have been disabled).
For this reason, it won't be rare to see level 80s using lower level items that share similar stats, or sometimes, better stats and more gem slots.
From levels 59+ the main goal in gearing is having as many gem sockets while not sacrificing too much on your secondary stats.
However. When we are strictly talking about instanced raiding, there is some hidden buff that incentivizes using raid gear. For example taking ICC25H in only level 80 runs, using ilvl 277/284 (using old numbers here just for you to understand) gear will benefit you more damage wise.
Additionally, we have a raid group that runs weekly Herald of the Titan runs on alliance-US
@jwl
Finally, you can use my armory link to my rogue. I try my best to keep him updated on the current BIS. I usually am mut spec but your gear will still be similar.
https://worldofwarcraft.com/en-us/character/velen/Questions
P.S. kudos if you have helmet enchants. Use those.