I highly recommend paying attention to https://docs.peachpie.io/compatibility-status/ -- there is still a lot of work to be done, and they are comparing to a really old version of PHP. There have been a lot of new features since 8.0.
Amateur here. This is good for what? Why somebody should use this instead of normal?
Migrating a legacy PHP code-base to .net maybe
IMHO, besides the fun to create such a project (and all the thibgs you learn while doing it), it's not for much. It tries to bring a technology somewhere (presuambly the desktop, as asp.net and PHP are already comparable) it's not designed for - which will bring you in trouble sooner or later. It's like JavaScript on the server, it's ok but there are languages better suited for this environment.
It's much faster to learn C# in the long term than to run PHP on top of .Net.
I'm not sure why anyone would use it, but it was probably a fun project to make. I do think the statement on their landing page which reads: "Compile and run PHP on top the modern, secure and highly performant .NET runtime" perhaps is a little disingenuous. This might just be me, but I read it as though they imply that PHP isn't those things, which would be a silly statement to make in 2024.