But a graphics card can't be worth $0 like a cryptocurrency. Even the RX 580 8 GB graphics card can play many modern games and its price will not fall below $100 if it is in good condition. Even if it is cheaper, then what price will the RX 550 2GB have? RX 560 4gb? RX 570 4gb?
I agree with your general idea, but I don't agree that we are anywhere near the price floor for current-gen video cards. RTX 3060's are selling for $330 used, but let's say they end up at $200 in 3 months if today's coin prices stay steady. That is a capital loss of $130 / 90 days = $1.44/day.
You will get $0.60/day of profit mining CFX at free power. That won't compensate for the $1.44 in capital loss. So the most profitable decision would be to sell that RTX 3060 today.