Research administrator here, so my perspective is from the university and not from a researcher. There is a way to check the status by whoever is PI or Co-PI. If you are Senior Personnel, but not a Co-PI, then it will not show up in research.gov for you at all. It's as though it's not your proposal.
As you can see in the screenshot of research.gov below, it takes a lot of time for them to review most standard proposals. I would never assume an award will happen within six months unless it's specifically an expedited call that is focused on short turn-around, which they normally say in the call. I actually assume either a year for larger centers like MRSEC, AI Institutes, Expeditions, etc. or for general calls, 6 months is the minimum, with NSF most likely to dump their budget in the summer before the end of the FY. In the screenshot below, there is a pending proposal since December. I am not going to ask the PI the status of the proposal until October. I should specifically note that proposals 1 and 3 are to the exact same solicitation, and yet have different status dates.
If your proposal was RWR (Returned Without Review), in my experience, NSF notifies you of that. This was much more common with FastLane and is less likely with Research.gov which has automated checks for many things. You should check your solicitation for RWR criteria. E.g., if you were required to include an evaluation plan, and didn't, they are allowed to RWR. This type of checking prior to submission is the job of your sponsored programs/research administration team. Technically, NSF reserves the right to RWR anything in the checklist in the PAPPG, but that doesn't mean they do it. My institution is an R1 school that has been called out for having et al in the references as a reason for return without review. I used to work at a smaller university, and had never heard of such a thing. But if you check the PAPPG, it is in fact a requirement to list full author names, and they do say anything in the checklist that is not fulfilled is subject to RWR.
![Research.gov screenshot](https://cdn.statically.io/img/i.sstatic.net/82exA2lT.png)