No. If you want only one package from contrib, you can add the repo, pin it below your others, then pin scrcpy from contrib above the others. That should do what you want.

https://wiki.debian.org/AptConfiguration

I can do something like this:

[\ #84]  apt-cache policy scrcpy
scrcpy:
  Installed: (none)
  Candidate: 1.25-1
  Version table:
     1.25-1 500
        500 http://deb.debian.org/debian unstable/main amd64 Packages

And it tells me that, for me, scrcpy is available from the main repository in unstable. Not sure how to find a package if it isn’t in one of your sources. I guess you could search for the package at https://packages.debian.org/index.