We are pretty free to use any ability that is related to the task and we get proficiency as normal and if it relates to our backgroundOne of the tools available to GMs and players in 5E is non-standard combinations of ability scores and proficiencies. It doesn't come up very often in my experience, but sometimes odd pairings make for interesting moments in play -- or, rather, interesting moments in play call for the odd pairings. I remember having PCs make Charisma (Athletics) checks to entertain a crowd in the arena, and have sometimes let them make things like Intelligence (Stealth) to try and surmise how an assassin or thief infiltrated a crime scene.
Relatedly, I sometimes let players make checks with proficiency based on their backgrounds or their class (and choosing an appropriate ability score). The 5E proficiency list is narrow and specific and sometimes it is easier to lean on "secondary skills" from the AD&D days.
What are your thoughts on non-standard proficiency and ability scores?