I like Trilium Notes. It's rich text based, not markdown based, but haas most of the organiation structures of Obsidian. It doesn't have the user base nor volume of plugin support, though. It does have a canvas mode for inking, but it's a separate note type, not part or every note.
For a purer inking environment, look at Xournal++. It's not as feature rich as OneNote, but it has the basics.
Or, you could try running OneNote with WINE. It looks like you'd have to use OneNote 2010 or 2013, though.