Downgrade Dune/Opam OR workaround for dune build

I have just installed ocaml, opam and dune on my computer and tried to run a new project using

$ dune init project calculator$ cd calculator/$ code .

which creates the project and opens it in VS Code. But when I try build and run the project withdune exec bin/main.exe or with dune build in the terminal, I get this error message:

File "dune-project", line 1, characters 11-15:1 | (lang dune 3.14)               ^^^^Error: Version 3.14 of dune is not supported.Supported versions:- 1.0 to 1.12- 2.0 to 2.9

Is there a way to downgrade dune to 2.9?

Thanks in advance!

Now I tried to update opam to the newest version with:opam update && opam upgrade, but I get the message that I have already installed the newest version 2.1.2-1.

My dune version is: 2.9.1My opam version is: 2.1.2