I invite you to have a look at my application SilentNotes;
It is a FOSS application which I have developed with a strong focus on privacy.
The notes can be synchronized end-to-end encrypted between multiple Android and Windows devices and can be self-hosted. Currently supported are the FTP protocol, the WebDav protocol, Dropbox, Google-Drive and One-Drive.
Evernote is another cross-platform solution which I've used for almost 10 years.
It has versions for Android, iOS and Windows;
In Windows, it can be installed both traditionally via a wizard and as an UWP app via Windows store (just go to https://evernote.com/download on your device).
You can find more information regarding privacy and security here. It ...
I have been using Simplenote and Standard Notes for years.
Both are FOSS and have their own mobile apps. For desktop I use their web editor, but they also have Windows app if you want to use it in desktop while offline.
There are some Google solutions I think might help.
Edit: they all need a Google Account (Login) so it dosn't meet all your requirements.
Google Maps has also a "share location" function, but not an "emergency button"
Probably preinstalled Google function called family link
Google Trusted Contacts Android App
I have spent some hours under this issue and via lots of testing I found that when you put a white border around the aztec code image, then it works quite well and fast :-) I use it in my app: //for the barcode bitmap (string) scanning: implementation 'com.google.zxing:core:3.3.3' //FOR THE CAMERA SCANNING: implementation 'com.journeyapps:zxing-android-...