Make a Support ticket immediately.
Tell them to un-remove all the games that were just removed. If you know how many you had that might be helpful.
Also while you're at it, change your steam password right now(and remember it) then click the Settings->Security->Dauthorize Devices button(before your hacker can do so). That will also log you out of your phone(Steam Mobile). Anyway, go through the login process with the Steam Guard code/QR code and THEN make the support ticket. Hackers usually close your support tickets if they still have access to your account.

There's a longer list of steps to secure your machine(remove keyloggers, etc) and I'm certain that will be posted here soon.

Hijacked. Malware or phishing.

Follow steps 1-6 to secure your account:

1. Scan for malware https://www.malwarebytes.com/
2. Check that the email and phone number on the Steam account are still yours.
3. Deauthorize all other devices https://store.steampowered.com/twofactor/manage
4. Change passwords from a trusted/clean device.
5. Generate new backup codes for your Mobile App https://store.steampowered.com/twofactor/manage
6. Revoke the API key https://test1.login.steam.hlxgame.cc/dev/apikey (there should be nothing in the APIKEY)

Regarding items:
https://help.steampowered.com/faqs/view/3B6E-B322-2400-8D24
If said items were from CS2:
https://help.steampowered.com/en/faqs/view/365F-4BEE-2AE2-7BDD

To restore missing game/s:

• https://help.steampowered.com/en/wizard/HelpWithGame
  
• Enter name of the game in search bar,
  
• Click on game,
  
• Click on "it's not in my library",
  
• "Restore removed package".

u right, when i post ticket he remove instant,, i alr doing deauthorize, change password and email, also revoke APIKEY, but my new ticket can't get answer or get access to install my game

ahh i can restore missing game now, thanks buddy