I tried for hours to redirect every pages of a folder to new url, matching the folder but it seems I definitely do not understand nothing to regex and redirect !

I want to redirect any pages into the folder /folder/ to a totally different url
Something like

RedirectMatch 301 ^/folder$ https://www.mynewdomain.com/id/2176

in order to redirect https://www.myolddomain.com/folder/123.html to https://www.mynewdomain.com/id/2176

I do not want to keep anything of previous url, just redirect any page of this folder to a specific url.

Someone can help ?
Thanx

I tried

RewriteEngine On
RewriteRule /folder/ https://www.mynewdomain.com/id/2176

but it do not work, i am not redirected when i reach an url containing /folder/. Tried

RewriteRule ^/folder(/)?$ https://www.mynewdomain.com/id/2176 [R=301,L]