I see now, that you were misunderstood in some parts.
even if I got reported a really weird bug related to UB, I should (I am not experienced enough to make a claim) be able to know it’s UB since the game’s gonna crash when I try to recreate the bug in Debug.
This may be problematic for several reasons: it may be hard to reproduce, the more complicated the state, the harder; bug may rely on some race condition that may be much rarer in Debug because of speed difference; UB is notorious for causing things that should (seemingly) never happen, like returning from infinite loops, proving false statements true, and such, so it may be hard to understand what at all happened and why.
Regarding optimisations, it might still be better to try to profile the code (I will be honest, I don’t do that until the moment when I can’t go further without optimisation, and I haven’t reached that with Rust) and see what are the real hot spots that require optimisations. I hope that someday you will be able to upgrade your machine, and hope that your game will be a good example of something that really runs anywhere
Well, they will try to eat everything they can reach