Why I can’t start rank? Why I only can play lone wolf with my account?

I think you are playing free fire in pc emulator. I have noticed that in recent times pc players no longer play br rank match also in cs rank you have to invite 3 more players then you can play free fire this is the main reason you are not able to play other modes other than lone wolf.

Free Fire rank match issues on PC happen because emulator players are restricted to prevent unfair advantage..

Because Free Fire is a mobile game.
When you play it on PC using BlueStacks, the game detects the emulator and often forces or affects ranked match behavior (like starting issues, delays, or limited matchmaking) to keep things fair against mobile players.