Notes: Any way to back up notes & folders?

For 4 years I have been using notes extensively, for my important research, admin and records, owing to it’s simple convenience. I have thousands of notes, categorised by many folders and subfolders, that I add to daily. I have become increasingly concerned that I need to backup to somewhere more solid than time machine, but the only option I can see is to export every single file as a pdf, which would be insanely laborious and messy. I’m worried that I’ve unknowingly set myself an impossible task by using notes for everything.

Does anyone have any idea how I can back up all my files to an external source/ drive, at once and on a regular basis? And is there anyway to back up my notes intact with folders and subfolders?