I don't understand (possibly because I lack Angular experience): what is it about a .NET backend using HTMX that requires presentation concerns to be mixed with business logic?
Don't you have to maintain that separation either way? Your core/application logic shouldn't know how its result is ultimately represented. That could be JSON or HTML over HTTP, Protobuf over a TCP stream, or a custom binary protocol over a Unix socket.
Obviously those representations matter at the presentation/transport boundary, but why should choosing HTML force that concern into the business logic?
Don't you have to maintain that separation either way? Your core/application logic shouldn't know how its result is ultimately represented. That could be JSON or HTML over HTTP, Protobuf over a TCP stream, or a custom binary protocol over a Unix socket.
Obviously those representations matter at the presentation/transport boundary, but why should choosing HTML force that concern into the business logic?