What is a power user in this context? Someone deeply familiar with Windows and has tons of Windows related setup/applications?
That doesn't sound like a government worker... They rely on Microsoft Office, but the actual operating system could be anything. The only non-portable application is video games really. While LibreOffice may not have complete excel functionality, the vast majority of functionality can be replicated in web apps/libreoffice. And frankly most of this work can be migrated to AI.
You can even skin Linux to look exactly like Windows if you want, or use Mint or something. But really all people need is to be able to open up Chrome and Excel.
I imagine the biggest thing they need to open up is Outlook.
In fairness, the transition away from MSFT 365 Copilot (as we all of course call Office now) might include more friction. Mountainous VBasic monstrosities are sometimes the way things get done in orgs I am personally familiar with and that can be hard to switch away from. In general though, I consider this focusing on edge cases as just not helpful, especially as one must start a transition to fully uncover them and get to addressing them too. I also don't think that ancient Excel scripts are an unsolvable problem, but one that needs to be very carefully handled.