I accidentally overwrote CMS pages when I migrated from M1 to M2. I still have the backup of the old M2. So my question is, where can I find the file location of the M2 CMS pages?
Just open your database managers like PHPMyAdmin or adminer and search for a table with the name cms_page (in your dumped back-up). And check every page via its name, for example, 404 Not Found. After this, you can see a column with the name "content" - its the content of this page, you can edit it. Screenshot example below.