There are a number of seriously conflicting stories. Some of them say "the cards were individually tuned and undervolted to run at maximum efficiency to make the most money so they'll be fine" and some say "these cards were overclocked and left to run in a boiling hot shipping container then they washed them off with a water hose".

Results may vary.

But I used my Radeon RX 6700 XT for mining nearly 24/7 for about 10 months (between purchase and when it paid itself off), while using it for gaming in between (I'd obviously stop mining). It ran around 65°C during that time. Very low core clocks, but memory was run at close to the maximum recommended speed by AMD's Adrenalin software. At least so far no signs of any problems.

LTT goes over it pretty well (IMO): https://www.youtube.com/watch?v=hKqVvXTanzI

tldr: Cards (like any piece of other electronics) do have a lifespan, but mining doesn't affect that. Cards that are kept clean and in better working conditions will run faster.