If a character has at least 11 Rogue levels, they get the "Reliable Talent" class feature.
Reliable Talent
By 11th level, you have refined your chosen skills until they approach perfection. Whenever you make an ability check that lets you add your proficiency bonus, you can treat a d20 roll of 9 or lower as a 10.
What happens if you then Roll a Nat 1 on a roll with which you would add a proficiency bonus? Is it neutralized or is it a Critical Fail?
In 5th edition, ability checks don't typically automatically succeed on a 20, or automatically fail on a 1. It's only attack rolls that have automatic failure or critical success.
The only rules relating to critical success or failure for ability checks is on page 242 of the DMG:
Rolling a 20 or a 1 on an ability check or a saving throw doesn't normally have any special effect. However, you can choose to take such an exceptional roll into account when adjudicating the outcome. It's up to you to determine how this manifests in the game.
However, Reliable Talent would bypass this. The wording of the ability says that you treat any roll of 9 or lower as a 10. Effectively, you totally ignore the number on the die and instead treat it as if you rolled a 10.
