Here's my list that I avoid if and where I can. As with everything, things are nuanced and complex, and it's not like every company I personally boycott is outright bad or good all around. I wasn't going to write down the reasoning for each and every one, but ask away if you want to know about the reasoning behind particular ones. I'll also note, this is 100% not in any order (other than as they came to mind), it was time consuming enough making this vs. ranking them all!
Disney
EA
Volkswagen
Tesla
BMW
Audi
NVIDIA
Nintendo
Google
Apple
Facebook
Shell
Microsoft
X
Discord
Reddit
Old Spice
Costco
Netflix
Spotify
Nestle
Toyota
Tencent
Blizzard
Uber
DuPont
Fountain Tire
Walmart
Boeing
Brave
Princess
Moxies Group
Hewlett Packard
Amazon
On the flip side, companies that while not perfect, I think overall are doing good things that I try to support when I can (if only with word of mouth in some cases):
Valve
Framework
Firefox
Pine64
Raspberry Pi
Hyundai
Lucid
System 76
A&W
Trail Tire
Plex
Amanita Games
iBroadcast
Volvo
Napa
Fairphone
There's probably more I'm missing, I'm a pretty strong believer that companies rule most of the western world and that if individuals want the world to meaningfully improve, we have to vote with our wallets as diligently as we vote at the polling stations.