Nemo still doesn't have folder thumbnails, which is an odd omission that I feel like shouldn't be that hard to implement. It's one of the few things I miss from my windows days when navigating through my albums
Is that a Windows feature? I've only ever used macOS and GNU/Linux so never got used to that. I just did a quick search on their Github Issues page and didn't see it requested. You can file a request here: https://github.com/linuxmint/nemo/issues