I've used Flatnotes for about a year or so and if all you want is to write notes in markdown and search them it doesn't get much simpler. It has tags and decent search, but other than that nothing. Easy to sync or backup though with a single folder of text files.

https://github.com/Dullage/flatnotes

Just curious, since I think they have the same focus, have you also tested SilverBullet?

https://silverbullet.md/