Should you use "at" or "onto": There is no fix rule per se, and mostly it's a matter of opinion and context, we tend to use one preposition over another. There are many exceptions and overlapping situations.

And if you wish to use a proper idiom, then,as explained,use: to take a backseat to put it on the back burner.

Alternatively, use COCA.

Should you use "at" or "onto": There is no fix rule per se, and mostly it's a matter of context, we tend to use one preposition over another. There are many exceptions and overlapping situations.

And if you wish to use a proper idiom, then,as explained,use:

to take a backseat

to put it on the back burner.

Alternatively, use COCA.