There are many different types, colors and finishes of edge paint based on acrylic (which is a type of plastic.) I like the more natural look of the vintage
Coach edges on the older bags, but I appreciate the finished edges on higher end modern bags too. Here's a tPF discussion:
https://forum.purseblog.com/threads/black-edge-paint-yay-or-nay.976664/s
Interesting thread on edge coatings here for the technically minded:
https://leatherworker.net/forum/topic/31788-rubberlike-edge-coating-what-is-it/
"Fenice leather edge paint and similar professional brands are based on synthetic polymers, so they are in a sense a plastic. Most major fashion houses and high end brands use this for their goods. The main reason is that most use chrome tanned leather and this doesn't burnish, but it's not unusual to see veg tan with painted edges too. The reasons for this is mostly down to production, as larger manufacturers rely on machinery, including 'edge paint machines' for their leather goods. Among crafters the use of painting edges often have a bad reputation and many accuse cheap brands covering up low quality leather and vinyl with paint. And while this is not entirely untrue, the fact remains that in some instances there are no alternatives, and done well - it can look amazing."
And I found these tutorials interesting:
https://www.goldbarkleather.com/sourceblog/2015/12/29/a-basic-guide-to-burnishing
https://www.goldbarkleather.com/sourceblog/how-to-use-edge-paint