Valve also doesn’t use shopping platform monopoly methods such as artificially making process low by selling at a loss, which is the main problem with other monopolies like Amazon.

That isn't the only method. There is also the "[Platform] Most Favored Nation" clause, which eliminates the ability to undercut the platform elsewhere. This allows the platform to leverage it's market share and benefits to maintain dominance, raising the price floor of the market so nobody can compete on cost. Being the dominant platform, with better economies of scale and consumer intertia, this gives them an advantage in that competing platforms have a difficult time being the better choice.

Valve uses a PMFN clause. See my other comments for links to relevant court cases.

The moment steam starts enshittifing, it will be very easy to switch to another platform. Compared with other platforms, like any social media or YouTube.

Being familiar with "enshitify", you should go read more of Cory Doctorow's (who coined the term) writing over on pluralistic.net. He writes frequently about monopolies (his writing on Amazon's monopolistic practices (skip to the part about high fees and raising prices) are applicable to Valve's PMFN clause). He also has explicitly given social media platforms as examples of platforms prone to enshitification because of the high network effects.