I fixed this issue by replacing the 450 Nvidia driver to 455 driver as you mentioned here. Now Steam is working properly and I can play my games again.
For those who wonder how to update the driver, follow these instructions, but before doing
mhwd --install pci Your455Family and right after doing
pamac remove for each driver installed (including the 450 driver) - which you can list by typing
mhwd --listinstalled - you also have to uninstall each of the driver installed (ex. for removing the 450 driver:
mhwd --remove pci Your450Family). This last part is not mentioned in the linked tutorial, but I had to do those steps to be able install the 455 driver.
I’m using Kernel 5.4.72-1 LTS (Recommended).