(I don't know too much about nuclear level situations so I can be obviously wrong perhaps but here's my take on it)
> supply chains to drop us into a multi-decade or multi-century dark age,or maybe cause a nuclear winter, although the actual risk of that is unclear.
It's defintiely gonna be a hard life if WW3 ever happens but I think with hydroponics and other advancement, a localized community can still have chances of making sense of things.
It definitely wouldn't be this life where we can eat almost anything but it won't be starvation either, hopefully.
For water, we might have to do reverse osmosis or boiling+condensing to remove radiation.
The biggest issue to me seems energy. Solar energy might be hard to get if nuclear storms are made over any region which I do think iirc can even stay till decades.
Temporarily Windmills and then primarily Hydroenergy is still possible tho but it might take some time to rebuild it if it got destroyed by Nuclear attack so energy to just produce food/water is possible but everything to me feels like it would be strictly rationed. You might have some spare energy for Radio.
I am not sure how food is gonna be distributed, perhaps a new system of work would be designed within community where community gives food and you give what the community might need to get work done.
I feel like though we are gonna slowly improve our Energy situations and as we do that, society can progress back to say a mathematician who can work on theorms which might require computers/energy and just computers in general back.
The quality of life would drop but I would consider tho that the people already in war-struck regions where they don't know if they are gonna be the next target of a messy war have their Quality of life significantly dropped as well.
Now the virus point is something that I don't exist similar to Lukan's comment tho.