Rosetta 2

It is free, and will install automatically IF (and only if) you need it to execute an x86 Mac program on Apple-Silicon M1.

For more information ➡️ If you need to install Rosetta on your Mac - Apple Support

As for the QLab app: Is QLab compatible with the new M1 processors?

Starting with version 4.6.8, QLab is compatible with macOS Big Sur and Apple Silicon-based Macs.

Which in aggregate means Rosetta 2 is available to you, but is seemingly not necessary if your QLab version is new enough.