In simplified terms:

You are allowed to modify stuff but it is not actually changing the install as is.

This is achieved by different techniques like file system overlays, containerisation, btrfs snapshots and so on.

The idea is to replicate the classical behavior you know from embedded devices that have their core functionality in ROM with even firmware updates only overlayed or modern smartphones: You can modify your system but in the end there’s always the possibilty to “reset to factory settings” as in: the last known working configuration.

You are obviously not doing enough work with a full screen terminal being open… 😜

Compatibilty of Windows games in Linux have gone a long way, partly but also independently from Steam’s work on it.

In fact Linux nowadays supports more Windows games than Windows, as especially older games still work there but not on modern Windows anymore.

I will not pretend that there aren’t games with issues, but in the vast majority of cases that’s new games and for the simple reason that some publishers actively go out their way to prevent them from working on Linux (highlights being anti-cheat tech that Linux worked hard to make it compatible, yet with certain publishers intentionally not setting a simple flag needed to run, often with totally made-up “reasons” about Linux’ insecurity…).