Full HD from a good camera is better than 4K from a poor camera. Lens, sensor, processor, codec and compression... everything matters.

So you're actually asking two questions in one:

1) Is 1080P (full HD) acceptable?

Yes, it is. All stock sites that I know accept it.

2) Is the DJI Spark camera quality acceptable?

I don't know this model so I can't answer for sure.

(Looking at movies from this camera on YouTube, it seems a bit soft and real resolution is probably less than nominal. As expected from a small and cheap camera. May be acceptable in very good lighting conditions, if you already own this drone why don't you try?)

Yes, it will be accepted, you can give it a go.
As other have said before, you will get decent results only in extremely easy light conditions. Forget anything even remotely against the sun or high dynamic situations.

The better the equipment, the better chance of being accepted.

Everything is constantly updating.

Several years ago (i.e., 10 years ago) - it was the "norm" to accept 720p (1280x720). And that was considered really 'good', also because that's what a lot of high end digital cameras did.

Now - if you tried submitting that - most likely automatically rejected because its too 'small'.

The spark (although I haven't used it) - is most likely just an "okay" camera. You will get some of the stuff accepted - but like others have said - if it isn't a beautiful bright sunny day - most likely you'll have artifacts (blocky pixellation) - which will get rejected.

So if you want the best chance of getting accepted - right now the mavic 2 pro seems to the best.