If this did not solve your issues, here is one more to try:
In “Controls”, try adjusting the reactivity setting for the rudder.
I have heard of settings between 20 and 65%
Keep taxi assist off for now.
Here are some taxi “helps”. It takes practice, and lots, as they (especially the 74-787) are quite fussy, apparently even IRL.
Use very little power, just enough to move.
When going into a sharp turn, do not turn the nose wheel 90 degrees, use a larger turn radius.
Avoid adding power in a turn if at all possible.
Speeds approx 5-10 kts in corners, the slower the better, don’t overpower or you will plow through the corner, as the nose wheel won’t dig in.
This does actually happen IRL.