report error

[manuel76413]

c:\dev\vcpkg>vcpkg --overlay-triplets=..\my-vcpkg-triplets --overlay-ports=..\my-vcpkg-ports install alphaplot:x64-windows
Computing installation plan...
error: while looking for qtbase:x64-windows:
error: while loading C:\dev\vcpkg\ports\qtbase\vcpkg.json:
$.default-features[11]: mismatched type: expected an identifier
$.default-features[12]: mismatched type: expected an identifier
$.default-features[15]: mismatched type: expected an identifier

[Neumann-A]

error: while loading C:\dev\vcpkg\ports\qtbase\vcpkg.json:

That is an error with your vcpkg checkout/version not with the overlay. Maybe you also need to re-bootstrap vcpkg itself?