Epic Game Store has one or two free games a week which are usually of decent quality. It’s a separate, and competing, client from Steam. Coincidentally, the current free game (until tomorrow so get it today if you want it) is PC Builder Simulator, an amusing game about owning a PC repair shop and assembling/fixing PCs.
There’s a thread in the Games forum for free PC Games that gets updated as something comes up though those run the gamut from little janky indie titles to decent AAA games to ancient game relics. Free though!