Rewrite domain.com/page.html to /page/

Hi guys, i hope you can help me with the following:

I have a website previously built in frontpage, and therefore all the urls have the following syntax:
https://domain.com/page.htm
https://domain.com/parent/subpage.htm
https://domain.com/grandparent/parent/anotherpage.htm

How do I write a rewrite rule that 301 redirects to:
https://domain.com/page/
https://domain.com/parent/subpage/
https://domain.com/grandparent/parent/anotherpage/

With rewrite rules in .htaccess.

I also have another site which I’m migrating soon from Umbraco, in which case the pages end with .aspx instead of .htm, but I figured the “fix” would be the same.

I’ve tried a couple of fixes posted here and other places on the internet, but none have worked so far.

Any help would be appreciated.