There is no firmware lock, and here's the iFixIt guide for doing it.
> How to Replace the SSD in your Mac mini (2024)
https://www.ifixit.com/Guide/How+to+Replace+the+SSD+in+your+...
There is no firmware lock, and here's the iFixIt guide for doing it.
> How to Replace the SSD in your Mac mini (2024)
https://www.ifixit.com/Guide/How+to+Replace+the+SSD+in+your+...
...normal M.2 SSDs are incompatible.
This guide is purely instructional for how to replace the SSD with another of the same type.
You can indeed purchase third party replacements up to the maximum size supported by that model.