P versus NP
Determine whether the complexity classes P and NP are equal by proving or disproving the existence of a polynomial-time algorithm that decides every language in NP, or equivalently by establishing that P = NP or P ≠ NP within the standard Turing machine model of computation.
References
For example, the famous Clay prize question of whether $#1{P} = #1{NP}$ --- widely considered one of the deepest and most profound open questions in mathematics --- concerns the properties of Turing machines.
                — Implications of computer science theory for the simulation hypothesis
                
                (2404.16050 - Wolpert, 9 Apr 2024) in Appendix A: Turing machines