Perhaps give something like this template a try. Its purpose is to minimise Scrivener’s project window down to only what is necessary to take notes quickly, and without ado. You can keep this open alongside other projects, or all on its own if you’re doing other things. I realise it’s not a different name in the toolbar, but the “interface” between this project and a more typical one is so different I feel it would be easy to ignore that.
It wouldn’t be saying anything too revealing about the new program, as it is talks about it in the blog post linked to above, but it is not RTF-based.
Most tools of this nature, these days, are not going to be RTF-based. It’s just too difficult to work with; you need to have a really good reason for investing huge amounts of time into the text editor (and working around the myriad labyrinthine bugs in the ageing frameworks that use it). Simple fact: it’s a 40 year old format that was discontinued almost 20 years ago. Even Microsoft Office doesn’t support it on iOS, and that suite is the whole reason that format was invented.
I think a simple way of putting it is that it’s not going anywhere any time soon, but there is no future in it either. It would take a rare developer to start a brand new development effort in 20256, with bright-eyed enthusiasm about using RTF as its core data format.
Funnily enough, if RTF is your constraint, I think Scrivener may be one of the better tools for the job these days (at least on the Mac or Linux, I know very little about Windows software in this genre)! While this was never its original intent, it is no slouch at being a core note-taking tool. Of course a lot of where that post links to goes way beyond light-weight, but that’s why I suggested just checking out the “scratch pad” template. That can be the beginning and the end of the journey, if that’s all you want.