The easiest way is to just drive it. You need a "certain tolerance" for minor wear and tear and bumps to your car and some cars are better suited than others, but with a bit of patience and by taking your time you can pass by a lot of roads with a 2WD. For example I have a stick shift Civic, I'm quite happy going on lots of really bad roads here in BC.
Then again, if I had a brand new Tesla, I wouldn't be doing this.
Most of the time, our unpaved forestry service roads are somewhat OK to drive on with 2WD. Because we have a lot of recreational hikers, fishermen and hunters, we also have a local publisher that sells printed maps covering the whole province with a lot more info about road conditions than you would ever find in a normal road map. Could be you have something similar in your area.
Typically what will happen is that a road starts out OK and then gets worse as you go on. If it starts out bad, then it will almost never get better.
Hills or mountains are also an indication of possibly bad conditions. If your road crosses a lot of contour lines, not a good sign. With hindsight too: I've gone up roads where the Civic, being a 2WD, literally was sliding backwards from it being too steep. Obviously, that can be dangerous on icy terrain or near ditches. But another risk is if you do manage to go down, going forward, but that extreme slope traps when you try to make it back.
Err on the side of caution. And that, includes, as Chris has said, paying close attention to how difficult turning around would be. If you had to reverse, how long would that be? If it looks like it would be difficult to abandon and head back, head back sooner rather than later.
When you find that you are consistently going over your tolerance, punishing your suspension, finding unavoidable pot holes or snagging on stuff underneath, best to back off. Also, don't do this at night, you can't see potholes.
Still "4WD-needed" is a relative term, esp in individuals' feedback. Most of our $$$ 4WD hereabouts have seen much less unpaved road than my Civic and I've had people warn me off driving an unchallenging 30m to a camping spot because I wasn't in a 4x4. Someone who does a lot of backcountry told me modern SUVs can be crap too: often meant for trips to the mall, too many have insufficient ground clearance.
Alternatively, you could drive up a while and then proceed on a bicycle. Road bikes are totally out but a solid hybrid or mountainbike can easily handle much rougher roads than a car can. That might require you to split up your hike into 2 trips: 1 road recon, 1 actual hike.
But often trail reviews will include everyone's complaints about the access road. Trail reviews without them hint at a tolerable road.
Last, but not least. Depending on your location, winter may not be the best of time to navigate too much in the backcountry. Consider taking along a 406MHz band sat rescue beacon and stocking your car with some emergency supplies.
In fact, since you've mentioned Covid already: our local Search and Rescue group strongly recommends people not venture in difficult terrain right now. Rescue ops necessarily involve bringing a lot of people together.