mfplat.dll
This file is not a system component: media feature pack for windows n editions. Restore it from the source that installed it rather than downloading a replacement.
If the file is already there and Windows still complains, read the message again: “entry point not found” is a different problem from a missing file, and installing the runtime again will not solve it.
And if the box says RUNDLL rather than naming a program, the fix runs the other way: something left an instruction behind pointing at a file that is meant to be gone, so restoring the file is the wrong move.
Do not download this DLL on its own
Searching for a missing DLL by name leads to sites that hand you that single file. It is one of the oldest and most effective malware delivery methods there is, and a system DLL from an unknown source is indistinguishable from a deliberately modified one. There is never a legitimate reason to obtain a runtime component that way.
The same goes for the tools that offer to do it for you: what a DLL repair tool can and cannot actually fix.
What it is
The Media Foundation platform library, which handles video and audio playback across Windows. It is present on normal Windows installations but deliberately absent from N and KN editions.
Where you see it: Video playback failures on Windows N editions, which are sold in Europe and Korea without bundled media components.
This is the one case where the answer is unusually specific and satisfying: if you have Windows N or KN, install the Media Feature Pack from Settings, Apps, Optional features, Add a feature. That restores Media Foundation properly. If you are not on an N edition, the file should already be there and a missing one points at damaged system files, so run "sfc /scannow" instead of downloading anything.
Why there is nothing to download here
There is no verified download we can offer for this one, because installing a file is not the fix. The steps above are what actually resolves it. That distinction matters: the sites ranking for this file name are selling a download that would not have helped even if it were safe.