I would recommend Joplin, for these reasons:
- It's digital (of course)
- It's cross platform: iOS, Linux, Windows, macOS, and Android
- It's fully open source
- It supports end-to-end encrypted syncing with different providers: Joplin Cloud, Dropbox, OneDrive, File system (for things like Syncthing), Nextcloud, WebDAV, S3 (Beta), and Joplin Server (Beta)
- It supports markdown editing
When looking for software in general, write down what you are looking for and what your requirements are. Then, consider if there are any conflicting requirements (e.g. "I want my handwritten notes to be transcribed, but I don't want any kind of handwriting recognition"). From there, you can make tough decisions or find a compromise. Then, think about any problems that may arise in the future. Do you plan to switch operating systems to something like GrapheneOS? Do you want to move away from cloud storage altogether? From there, you can get a good idea of what to look for. Good luck!