Was interested, and searched the store, didn’t find it.
Came back to the link to GitHub:
Xournal++ is a handwriting notetaking software with PDF annotation support. Written in C++ with GTK3, supporting Linux (e.g. Ubuntu, Debian, Arch, SUSE), macOS and Windows 10. Supports pen input from devices such as Wacom Tablets.
iOS is not listed- ah well.