Why does this map configuration work with Map, but not with ProjectTo

[nivle]

CreateMap<Src, Dest>()
.ForMember(dest => dest.ChildOfDest, opt => opt.MapFrom((src, dest, destMember, context) => context.Mapper.Map<IList<ChildOfSrc>, IList<ChildOfDest>>(staticFunctionThatReturnsNewChildOfSrc(src.ChildOfSrc))));

await mapper.ProjectTo<Dest>(srcContext...).ToListAsync();

When I use ProjectTo I get:

Unable to create a map expression from . (Src) to IList`1.ChildOfDest(System.Collections.Generic.IList`1[ChildOfDest])

Mapping types:
Src -> Dest
Src -> Dest

Type Map configuration:
Src-> Dest
Src-> Dest

Destination Member:
ChildOfDest

Meanwhile this works fine with the above configuration:

mapper.Map<IList<Src>, IList<Dest>>(await srcContext.Include(s => s.ChildOfSrc).ToListAsync());

Is it because the items when using Mapper.Map are already loaded in memory?
Or should that code als be able to work with ProjectTo, and this is a bug?
Or is it because of some other reason?

I also tried using custom value resolvers while using ProjectTo and the result was the same.

[lbargaoanu]

https://docs.automapper.org/en/latest/Queryable-Extensions.html#supported-mapping-options

[nivle]

Thanks, that not supported list explains alot :D