If your old app can export Markdown, Grape can read it. This works on desktop and on mobile, and importing is part of the Sync, Pro and Lifetime plans.
How it works
Open Settings, go to the Data tab and choose Markdown Files from the Import menu, or Import Markdown Files on the phone. Point Grape at the folder that holds your files. Every Markdown and plain text file inside becomes a note, and subfolders are recreated as folders in Grape, so the structure you had survives the move.
What comes across
Headings, lists, checklists, bold and italics, links, code and tables convert to their editor equivalents. Grape shows a count of what it found before it starts and a progress counter while it runs.
If nothing is found
Grape looks for .md and .txt files. If the picker reports that none were found, check that you selected the folder that actually contains the exported files rather than a parent folder with archives in it.
After the import
Give indexing a little time to work through the new notes if you use the AI features. Search by title and keyword works immediately.