Best advice to you without actually seeing the edge concerned about, is, check with a local millwork shop. They can make you a wood trim that will be durable and pleasant to the eye. If you have a good carpenter handy, any type of finish edge can be made with some craftmanship and time. Tip, you can soak wood in water to get it to bend if that is needed, hope you find what you need.

It's this kind of stuff, cut into suitable lengths and with screw holes drilled into it. Pound it into the ground and attach the retaining boards. http://www.homedepot.com/p/Crown-Bolt-2-in-x-72-in-Plain-Steel-Angle-with-1-8-in-Thick-42110/202183506 Or this slightly smaller stiff: http://www.homedepot.com/p/Crown-Bolt-1-1-2-in-x-72-in-Plain-Steel-Angle-with-1-8-in-Thick-42090/100338229

@SJ_McCarthy my contractor has vanished and left me wondering what he used for many things. He told me one thing but my “fixers” have told me that what he said was not honest and true. All I know is that we bleached the floors (took 3 days) and then stained them and applied a satin finish of some sort (oil based I believe based on the fumes). My current contractor says it’s polyurethane and needs to be completely redone with furniture removed and is removed for a few days. (Not an option at the moment). I did experiment on the 3rd floor by lightly sanding the floor and then Applying old masters gel stain and it looks so much better! Here are some pics of the before and after of the 3rd floor. I only tried this out because it’s what my contractor did on small fixes in my girls rooms. I thought I might as well try it it out on the 3rd floor and I’m wondering if I can do the same process myself in the kitchen? Or refrain?

Thanks for all the very helpful comments! I really liked the idea of using shellac and Zinsser SealCoat pre-mixed, dewaxed shellac looked like a really promising product, however, it is super hard to find right now (at least in Canada). It's either a COVID related manufacturing problem, or I think I read somewhere that there was a bad crop of lac beetles...! So I was ready to explore mixing shellac from flakes, but getting the right alcohol was proving a bit difficult too and would all have to be ordered online without the option of doing a small sample first. I was at Benjamin Moore and chatting with the lady who worked there and she suggested a water-based floor varnish by Saman (a Canadian brand I think). Just letting some samples dry right now, but it is looking promising! I'd be happy to hear if anybody else has had experience with varnish, I'm feeling like it might be a "too good to be true" situation. Seems to kind of be like a sweet spot between shellac and polyurethane (although it seems quite similar to poly from what I can tell/read). Because there's big cracks in between the subfloor boards, and nothing between there and the ceiling below, we're putting down an underlayment in hopes of creating a bit of a barrier (in the event of spilling water, for example, it would just go straight down to the ceiling below), minimize impact noise and keep the dust below the subfloor contained. Spent a ton of time researching alternatives to flooring paper underlayment for top-nail, plank wood floors, so just wanted to say thanks to @SJ McCarthy for their contributions on other posts which were very helpful. I've ordered QuietWalk and hoping that will fit the bill. QuietWalk Plus wasn't available in Canada but we don't need any moisture protection from the subfloor so hopefully QuietWalk will suffice. I called the manufacturer and they indicated it should be OK. Eventually we'll probably add insulation between the floors (it will likely have to be blow in from what I understand, since I don't want to rip out the ceiling and the subfloors upstairs can't be lifted because they span across load bearing walls) to help with soundproofing, but hopefully the QuietWalk will help reduce impact noise a bit. My husband and I spent a couple days removing 90 years worth of headless nails and tacks. Now we'll be spending the long weekend steaming the boards to try and close any small holes, then wood filler, making wood plugs, gluing knots and more sanding. Sometimes it seems silly to spend so much time on these low-quality boards, but I like that they're wood from a different era and can't imagine ripping them up and throwing them out. Nova Scotia forests are being clear-cut across the whole province, so I think it's worth the effort to salvage what we have instead of buying new if we don't really need to. Thanks again for the suggestions and feedback!