Joplin does not natively support regex searching. There is a Search and Replace plugin that appears to handle regex. I have never tried it.
The Joplin project owner is aware of the request for a regex search capability which is why it was put forward as a project in GSOC-2020.
Admittedly you have deleted the one from a couple of hours ago but please don't repeatedly "bump" threads if you do not get a response, especially if it's a feature request. You could always try searching the forum, which was how I found out about the Search and Replace plugin.