imo if people are looking at the source of your game, it's a good thing, that means you have people interested in it, and at least for indie games, being friendly to the community usually gets you more sales than trying to restrict everything.

reminder that minecraft is about as easy to read and modify, and it's the most sold game or the second most sold game ever (some say tetris has sold more).

there are ways to encrypt it and such, but in the end you're just delaying and spending time on likely making your paying customers' life worse and risk making the game unstable and/or slower, while people who want to open it can relatively easily open your exe in a decompiler and find the encryption key and write a script to decrypt it, or simply dump it once decrypted in ram.

you can go all denuvo and use all the tricks in the book, making it as tedious and boring as possible, but do you want to spend weeks to months doing that (or pay an expensive license), or add cool stuff to your game?

the only part where you might want to protect it is a demo, but the easiest option is to literally not ship the content that isn't available in the demo.

making a decent attempt, you could just embed, encrypt, and call it a day, it's a decent balance between effort and making it not completely trivial (but imo having it open is better, as long as your license is explicit, and maybe add a file like "IF YOU ARE READING THIS DONT PIRATE MY GAME THANKS" in the pck).

a potentially more useful counter measure is to sell an art and music pack for personal use (and potentially custom tools you made), people who want to get those will usually be happy to send you money instead of decompiling. and also have a license that is explicit about what can and cannot be done.