Coming at it from the support side of things (where I see when things go wrong or behave unexpectedly all too often), if you’re open to it, I would advocate for switching from relying on file mtime to a frontmatter-based modified time instead. The Linter community plugin can help with this, and even batch all those older files for you (make backups!).
The reason is that different operating systems, tools, and syncing services all handle modified times differently. It’s very likely that your current device and OS won’t be the final place you work with these files. By keeping the modified time in frontmatter, it’s stored with the content itself, versioned, and stays consistent no matter where or how the file is opened or synced.
Just something to think about.