As the reverse engineering communities will be glad to tell you, software basically is open source. It must eventually be decoded into instructions to run on a processor, and while it's not impossible to fully sign / encrypt the binary blobs before they are run, it is practically not worried about for most applications. Without using specialized hardware, you can at best obfuscate your code, but you cannot make it impossible to eventually disassemble and understand.

Assume your code will be disassembled at some point by a bad actor. Don't assume that any code distributed to a client is safe or trustworthy, and expect that any data, methods, or secrets contained in that code are now public knowledge. To secure your environment systems under any other assumption is a dangerous falsehood.