Pilot reported loss of aircraft control during taxi following landing rollout that resulted in a taxiway excursion.

Narrative

I was the Pilot Flying on Aircraft X from ZZZ1-ZZZ2 on Day 0. Halfway through the flight we received word that the ZZZ2 was shut down due to snow and snow removal. The weather had deteriorated badly. It was fine for our forecasted time of arrival and it didn't require an alternate. I didn't think to add an alternate either. After speaking with Dispatch; we decided that if the ZZZ2 airport was not open; we would divert to ZZZ. The weather was marginally okay; and it's a typical diversion airport for ZZZ2 as the passengers can drive over in an hour or so. The flight deck did get busy during the descent. We were estimating an arrival at ZZZ2 at XA:10Z; and the airport was supposed to reopen at XA:00; and I honestly expected it to reopen. We received a message from Center that the closure time had been extended to XA:30Z. At this point we elected to proceed to ZZZ. I had already checked the weather; the approaches; the NOTAMs and didn't see anything I didn't like. I also had the Captain phone the FBO in ZZZ to ask about ground conditions since there wasn't an ATC Tower on the field. The report was braking was medium and there was light snow. I elected to fly the RNAV (RNP AR) Y Approach. I landed uneventfully and it was a smooth touchdown and rollout. I maximized my use of the thrust reversers and didn't really utilize the brakes until I was below 60 kts. I'd say. I chose to continue smoothly decelerating and I planned to exit the runway at the end; at Taxiway XX. I handed the controls off to the Captain at a safe taxi speed and he exited the runway by very slowly making a left turn on XX; and then another slow left turn on XY. As I was in the middle of my after landing flows; I began to feel the airplane slide. I looked up and he was trying to turn left but the airplane was heading straight ahead towards the edge of the taxiway. Beyond the taxiway was a small curb; a fence and a small hill. I knew he was using the brakes fully; and he maximized his use of reverse thrust. I was convinced we were going to run off the taxiway; and by the time we had stopped I wasn't sure if we had or not. I was sort of in a state of shock at the time; and I think he barely just let off the brakes as the nose wheel steering tiller was all the way to the left; and the airplane began slowly turning on the taxiway. We centered the aircraft on XY very slowly. Airport Operations was on frequency and I told them to come down and check our skid marks in the snow to see if we had gone off the taxiway. They arrived and said we'd missed it by a half an inch. As we continued to taxi to the FBO; airport operations told us that XX was NOTAMed closed. I didn't recall seeing any NOTAM; and I told him that. He said he'd look into it. We parked and shut down without any further incident. Upon review of my outbound paperwork; indeed the XX closure was on my flight release paperwork. But I didn't have any paperwork for ZZZ for the flight in question. I was connected to my aircraft WIFI and I was using the Jeppesen App to look at the weather; which was updating fine. The NOTAMs never showed up; and thus I assumed there weren't any. Also complicating this was my fatigue level. It was a very early morning. I have had several minimum rest overnights in the last week and they really add up. I had already called in fatigued earlier in the week for a similar situation. But I felt rested enough to do this trip; and admittedly I felt a little pressure because I didn't want to call fatigue twice in one week. But the short overnights; early mornings and hectic days really take a toll on the crew members; including myself. I just wanted to get that plane from A to B to C so that I could get off it and get home the next day. The operations and scheduling were very taxing on me this week. I should clarify; that I was not in a state of fatigue this morning; but I was certainly not my best. I don't think either of us were. I encourage our weeks duty and rest to be reviewed. I have attached screenshots of my Jeppesen App where I was reviewing the weather and the NOTAMs for this flight. My suggestion is to alter our scheduling so that we do not have chronic minimum rest (or close to it) overnights with very early shows. I can adapt to time changes and body clock shifts; but these 10-11 hour rest periods with very early show times do not allow me the time to do this. The other suggestion I have is for the FAA and the NOTAM system. They are notoriously complicated; and very difficult to understand. More than half of them are absolutely useless and it's just more garbage to try to sort through. I need important NOTAMs to be published and displayed.