D&D 5E TOTM and flanking

As a player, I'd say "I attempt to move to flank (enemy) with (ally)." If the DM says it would provoke, I take that into consideration. As a DM, I think it depends on the numbers. If one side has twice as many as the other, flanking is automatic. If they're even, I'll give it a 75% chance of doing it without provoking, being outnumbered gives 50%, and outnumbered 2:1 is only 25% chance.

I don’t use flanking rules, but if I did, and I was using ToTM, I might give the creature/pc trying to flank a dex check vs dc 20 to see if they get into a flanking position. If they fail the check by 10 or more (or roll a nat 1) they tip off their intentions and can only attack that creature at disadvantage. I set the dc at 20 because I wouldn’t want it happening too often. Just a thought. I tried active choices like this during playtesting and I liked the way they worked.

I'm not currently running any editions which include flanking as a core mechanic, but in my 5E and old-school games, I will occasionally grant ad hoc Advantage to attack when players are ganged up on/surrounding a foe or when one has specifically maneuvered to attack it from a hard-to-defend quarter.