I want 500+ games on steam

I have 605 games judging by the badge Steam gives you.
When I first started PC gaming and Steam I got games via giveaways which were more plentiful but mostly trash low budget games. Tremor games where you did surveys and other mess to gain points and trade them for games. Most I got from there were decent but it went down in quality before it went belly up.
Game company giveaways during Christmas or other holidays years ago were a big haul.
Sega was giving away games for Valentines and there were some good titles and goodies in the mix.
Then I discovered SG which then lead to me discovering the world of bundles and third party key sellers.
You have sites that will sell games for dirt cheap if you're lucky but I think even those are dying out or straightening their acts so not so they can keep getting keys.
After awhile I stopped chasing just any ol' game o add to my library because of no interest, their lack of quality, or not worth the hassle.
Started spending money on bundle that are worth the money and never looked back.
But as someone mentioned at some point you end up not having the time to play most of them.

Amazon Prime gives out a half-dozen games every month. Combined with Humble Bundle, you should get 12-18 games per month.

Then there are the store bundles, and of course here.

There's some free games that add a +1 to your account I think. Look for ones that have achievements and DON'T say "Steam is learning about this." Try these. Someone please correct me if I'm wrong.
https://store.steampowered.com/app/361630/404Sight/
https://store.steampowered.com/app/530330/Blameless/
https://store.steampowered.com/app/409160/Dr_Langeskov_The_Tiger_and_The_Terribly_Cursed_Emerald_A_Whirlwind_Heist/
https://store.steampowered.com/app/823830/Frightened_Beetles/
https://store.steampowered.com/app/643870/Kitten_Adventures_in_City_Park/
https://store.steampowered.com/app/648390/Maries_Room/
https://store.steampowered.com/app/812810/missed_messages/
https://store.steampowered.com/app/467360/OffPeak/
https://store.steampowered.com/app/671720/Robin/
https://store.steampowered.com/app/758530/Sprout/
https://store.steampowered.com/app/1469280/SuchArt_Creative_Space/
https://store.steampowered.com/app/665490/The_Monster_Inside/
https://store.steampowered.com/app/250600/The_Plan/
https://store.steampowered.com/app/1241700/There_Is_No_Game_Jam_Edition_2015/

Just don't. It is completely useless. But if you have money to burn for games that you never will play, try allkeyshop. There you can find keys for less than a euro.

hmm - not quite sure what to make of your statements. I´ll take it word for word for now ..
given you´ve been on Steam almost 20 yrs I´ll just assume you know about SteamDB ?
well, here we go - goto steamdb, login, install their addon, and then ----> well there´s a script you can run via the site that adds every free license available in the region you´re in to the account you´re logged in with .. might take awhile, but there should be a couple of +1s in it for you
there will be an absolute crapload of other stuff too! (we´re talking several k license activations iirc)

so pls proceed only at your own risk and if you really want to

It won't make you happy.