I too am interested in an automated system taking data from things like smart rings/watches, ideally with home assistant integration. Do you mean like basic note taking? something like Joplin could be used for that. I use it extensively. It has a to do checkbox function, which you could use as a reminder, though it doesn’t pop up. You’d have to look at it. I think for reminders etc. you’d perhaps be looking at calendar software, perhaps next cloud, which also includes notes.