How to set up a 301 redirect by mask?

Question

htaccess

There was a site on Bitrix. As you know, it forms links in records without .html, but at the end / (slash)
Now they have transferred this project to another system, because Bitrix did not bring any benefit, it only loaded it superfluous.
The data was exported to a new engine with the SLUG URL saved,
but now .html appeared at the end of the link,
i.e. it was: site/method/page/
became: site/method/page.html
and the second section
i.e. it was: site/artir/page /
became: site/artir/page.html There
are about 1200 such pages, and therefore it is not possible to prescribe a redirect for each page, and therefore I am looking for an option how to do it by mask, because everywhere you just need to add .html