The Season 1 Uber Boss Echo of Varshan is great for farming gear! He drops between 1-5 items, guaranteed to have Item Power 800 and also Sacreds, with a Level 60 requirement, which is amazing for your alts.
You can defeat the boss before level 80 depending on your build power. Here are some video examples of Vashran dropping loot!
We also have a few Reddit threads, confirming Vashran drops at least 1 item with 800 item power.
Uber Varshan Guaranteed 800
by u/Dusaboro in diablo4
800 Item Power Sacred Legendary Legs Drop ?
by u/hanckerchiff in diablo4