I don't have a PS5, and I don't know how valid this is, but I've be seeing it go around:
https://twitter.com/frwololo/status/1610815598811914242
But 2 years in the consoles life, hardware experts from console repair shops are telling a different story:
According to 68Logic, a PlayStation scene member who owns a hardware repair shop in France since 2010, using your PS5 vertically can damage it permanently, and hes seen the result first hand with his clients consoles.
The problem, he says, is that the liquid metal used to cool the APU can sometimes spill, and become uneven, which impacts (at least) the cooling. Ben Montana, owner of specialized repair shop ILoveMyConsole in France, has also been trying to bring attention to this issue for months. He says these are not isolated cases. According to him, the risk is high for PS5s that have been standing vertically for a long time, and he says all models are impacted. This includes Digital edition consoles, as shown in the picture below (some people theorize that the vibrations of the Blu Ray drive could make the issue more severe on Physical Edition PS5s)
more at link