I assume you tried using Joplin as a to-do list app? IIRC it worked, but was too fiddly with the square brackets.
Tasks.org is an open-source to-do list app working with multiple providers. On first glance, CalDAV and EteSync might be something for you (ignore DAVx⁵ as it’s a worse CalDAV).
As for me I’m using CalDAV my mail provider mailbox.org is providing me together with Tasks.org on Android and Thunderbird on desktop.
For first few seconds, I deadass though they are talking about Germans with a height of 1,5 meters.
What about boolean though? /s
Do your services need to be reachable from outside right from the start? If not, get yourself comfortable with hosting, maintaning and backing up the server. Automate your backups as much as possible and recover at least once from a full backup to check everything!
This should give you a solid baseline to then think about exposing your services, which is arguably the scariest part, but can come afterwards.
I would say, it’s them caring about the product and their needs, rather than the underlying stack.