Like the back problems sometimes associated with rowing, a lot of knee issues from running are due mainly to bad form.

If you over-stride, particularly down-hill (and going "too fast" down hill instead of managing your pace/stride is a recipe for over-striding) the knees will be too straight during impact and so experience excessive impact force (and therefor potential damage) that would otherwise be absorbed by muscles/tendons/elsewhere.

While form is important, it doesn't fix fundamental joint problems unfortunately. I was checked fairly carefully by a couple of NHS physios, who both agreed it was joint problems, not bad form.

No, once you have a significant joint problem (from running or anything else) running is never going to help and will probably make things worse. Cycling possibly too, depending on the problem.

Swimming is probably the thing to go for in such circumstances. While some problems make that difficult too, it doesn't have the impact or strain (depending on stroke) of other options.