Found this:
Tackles are actually not defined as an official statistic by the league. What counts as a tackle is defined by the scoring crew for each stadium, so unfortunately there is no straight answer to your question as there are 32 vastly different viewpoints on how to score tackles. Some crews give out tackles like crazy to every defender in the same area code when a player goes down, some crews like padding the tackle stats of a single player on the home team even when he's nowhere near the play, and some crews are stingy with tackles and don't mind putting nobody down for a tackle if they aren't sure who should get the credit. If you watch games and try to match up actual tackles with what shows up on the box score, you'll find that they rarely ever match.
Seems like a tackle is in the eye of the beholder.
Also, have fun perusing this...
https://operations.nfl.com/the-rules/2020-nfl-rulebook/