If you want to access your notes and todo-lists from several computers and your mobile phone there are several tools you can use. One of the most flexible and transparent tools is Syncthing. You can set it up to sync specific files and/or folders and once done they will be kept in sync if you update the files on your computer or on your mobile.
In this documentation we will not go through how to set it up as it is well explained on Syncthings website.
Other alternatives could be using Dropbox, GitHub, WebDAV, NextCloud or other cloud storage services.