How to find out tag for using instead of "latest" in mcr.microsoft.com/powershell:latest?

Beginning of my Dockerfile is

FROM mcr.microsoft.com/powershell:latest

Now it is version which uses Ubuntu 20.04 with Powershell 7.1.2.
How can I replace “latest” with some tag to freeze image version in future?
How to detect this tag?

I need to continue using Ubuntu 20.04 with Powershell 7.1.2 in Dockerfile when mcr.microsoft.com/powershell:latest will have Ubuntu 21 and Powershell 8 for example.

On hub.docker.com

https://hub.docker.com/_/microsoft-powershell