In the most recent version of Elementary (6, Odin) I installed Steam using the Flatpak version and it worked well. The problem was that when I wanted to use Steam Play (trying to emulate Windows using Proton) my game wouldn't launch (I was trying to play The Secret of Monkey Island Special Edition.
It turns out Proton doesn't really play well with the Flatpak version of Steam, so I had to install Steam from the official .deb on https://store.steampowered.com/about/.
Installing via the .deb (I used Eddy) leaves a bunch of dependencies out. Here's what worked for me:
sudo dpkg --add-architecture i386
sudo apt-get update
And for the 32-bit drivers
sudo apt-get install libc6-i386
sudo apt-get libgl1:i386 libdrm2:i386
I hope this helps anyone trying to install Steam in 2021.