Beamer exporter not working (EDITED: 2023.05.29)

Problem and solution

While working in Emacs 27.1 I encountered on a problem that comes down to unavailability of exporting to beamer. So: :C-c C-e l b didn’t work. Besides when exporting a file I got unknown "nil" back-end error.

After many hours of searching and trying for example to explicitely import ox-beamer which seems to be embedded into emacs I finally found solution in the internet.

To solve the problem I needed to do:

C-u M-x org-reload

Another solution

It appears that beamer exporter can be enabled by

M-x org-beamer-mode