I have been using Notability Mac and IOS App, the App design and features are very good for note taking. For me, I did not use most of the features like handwriting, formatting and adding pictures.
Since I needed to migrate back to Linux, I searched and tested many Apps like Evernote (which naively not supported under Linux), but for the features I need which are.
1- Simple App to synchronize between IOS and Linux,
2- Search function.
3- Backup.
4- Ability for migration to Linux.
I found SimpleNote https://simplenote.com by Automattic.
It surprised me to be available for the "three" most popular desktop OSs, IOS, Android and also by using the browsers.
Even the App for Mobile and OSs is free (unlike Notability and many other Apps). With high stability and simple design
Migration from Notability to SimpleNote:
1- Since Notability backup notes to different cloud services. Choose from Notability options to backup the notes in PDF to Dropbox (also you can configure it for Google Drive and others).
Then download the directory from Dropbox.
2- Request Dropbox connects from SimpleNote contact form https://simplenote.com/contact-us/
3- Using "pdf2text" command under Linux, to convert all the PDF files to text files where SimpleNote recognizes.
This command will convert all the files within the current directory from PDF to TXT.
for file in *.pdf; do pdftotext "$file" "$file.txt"; done
4- After the request to connect to Dropbox added to your account, connect your SimpleNote with Dropbox from account's settings, then upload your converted text notes to the "SimpleNote" directory created in Dropbox. Finally, synchronize from account's settings, and it will download the text files from Dropbox directory in the App as notes.
A note received from SimpleNote support, if you remove the directory in the Dropbox, all notes will also be removed.