Plex for Windows has no built-in Plex Media Server.
Did you by chance at any time install a Plex Media Server on that laptop – maybe for some testing?
Anyway you can get rid of that entry (assuming you want to get rid of it) by removing the entry DESKTOP-B5MA51J from https://app.plex.tv/desktop#!/settings/devices/pms (don’t remove your actual server as that would mean you need to claim it from scratch).
Are you positive that you installed “Plex for Windows” and not “Plex server for Windows”?
Take a look into the “Apps” control panel of Windows, which is listed.
If the undesired server no longer appears in Authorized Devices and Plex Media Server no longer appears in Windows’ Control Panel → Programs & Features, try resetting Plex for Windows. You will have to re-pin desired libraries to your home page.
Our Plex app for Windows and Mac computers is a standalone application that has the layout of our regular web app, but pairs it with much more robust playback capabilities as well as the ability to download items for offline use.
A Plex client app for home theater users. It has an alternate UI called “TV Mode” which looks very much like the Plex SmartTV, AndroidTV, etc apps. Some users prefer Plex Media Player to running the Plex app on a Smart TV, Roku, FireTV stick, etc.