I think I've got tackling down now, kinda. Especially when it comes to players coming in from the side of the box and almost having a fit with how many times they try and turn you, like they're all Messi on acid or something.
I had no hope with any of them at firs but then I decided to pull back a tiny bit, like maybe two arms length away, and hover using the jockey button. It's kinda bringing more success. Usually when they make an attempt to cut back and run by you, you can double tap for the standing tackle and cut them out, unless they attempt to ground pass it into the box which seems to be about 50/50 for whether you'll block it at that point.
The main problem then is trying to both block the route for the various attackers in the box and still have someone covering the player with the ball on the edge of the box. You'll never have the time to get together a decent tackling position when it's passed to someone in the box, and my I seem to have a huge issue with covering runs and movement in the box while also making sure the ball carrier doesn't scamper away from someone I was using teammate pressure with IF I was covering in the box. So even if you do get a feel for tackling, it can still be frustrating.
Also, don't attempt to push someone off the ball from the side if you don't have any advantage over them when running in, in terms of position or speed. Especially if the player who has the ball has similar or better strength. I've stopped running towards them when they're starting to scamper ahead of me as that just means I'll get trapped in the animation of battling them until I slow down or trip lightly, and then they're definitely away. A tiny bit of distance to keep up your speed and attempt to get into a better position before going in for the jostle battle has worked better for me too.
Playing on Super Star, by the way.