Server commands not working

I have a vanilla server that I started and I cant use any commands. I type let's say /gamemode or /give /fly /tp it says unknown command and I cant use them. It says use /help for a list of commands and those commands are in the list yet I can't use it. I'm already opped

Quote from Roman

Which software and version do you use?

Did you already try to deop and op you again?

1.14.3 and vanilla I havent tried the deop I'll try it tomororw