Good afternoon mikulas80,
Welcome to the Apple Support Communities!
I understand you wondering why your videos are created as .mov files instead of .mp4 files. Are you asking about when you capture video on your iPhone or when you are exporting from iMovie for iOS or another app? The .mov files are the most compatible for Apple software. When you export a video project from iMovie or Final Cut Pro X on a Mac, the resulting file is a .mov file unless you specifically choose iOS devices.
How are you planning to use these video files? Who is your intended audience to view them?
Using HEIF or HEVC media on Apple devices
"Though capturing in HEIF and HEVC format is recommended, you can set these devices to capture media using the older formats, which are more broadly compatible with other devices and operating systems:
- Go to Settings > Camera.
- Tap Formats.
- Tap Most Compatible. This setting is available only on devices that can capture media in HEIF or HEVC format, and only when using iOS 11 or later.
- All new photos and videos will now use JPEG or H.264 format. To return to using the space-saving HEIF and HEVC formats, choose High Efficiency."
Take videos with your iPhone camera - iPhone User Guide
Export photos, videos, and slideshows from Photos on Mac - iPhone User Guide
Edit video in iMovie on iPhone, iPad, iPod touch, and Mac
Please reply to this thread with the additional information requested, and I'll do my best to help you with this!
Take care.