The UK does not automatically share criminal record information with any other country, so unless the police have an active interest in you, they won't be telling any other countries about you. Apparently, ETIAS will be voluntary until the end of 2022, then mandatory from the start of 2023, but it will rely on your honesty as to whether you disclose, as they will have no way of checking what you tell them. Once fifteen years have passed, you won't be required to disclose anyway, but if you travel without disclosing and later need a Schengen visa for work, study or residence, they will be able to see that you had travelled without disclosing, which could well count against you. If you're sure you won't need a Schengen visa at any point, then it's up to you what you do.
Robert Lightfoot, former head of NASA, said it succinctly in his parting speech in April 2018: Protecting against risk and being safe are not the same thing ... [W]e must move from risk management to risk leadership. From a risk management perspective, the safest place to be is on the ground. From a risk leadership perspective, I believe thats the worst place [we] can be.