iPhone 13 Pro: Cannot play or transfer large 4K video

You can try to use Image Capture on your Mac.

1. Connect your iPhone 13 Pro to your Mac using a transfer capable cable.
2. Open Image Capture on your Mac
3. Select your iPhone under the "Devices" list on the left.
4. Unlock your iPhone and tap Trust This Computer if prompted.
5. Sort the list of media by Size to easily locate your 30.94 GB 4K video.
6. At the bottom of the window, choose a destination folder on your Mac.
7. Select the video and click Import.

See this article for more information.

Image Capture User Guide for Mac - Apple Support

Probably you are trying to upload to iCloud Drive.

If you recorded 4K video on an iPhone 13 Pro (128GB) and are unable to get those videos into iCloud even though you have a 2TB iCloud storage plan, the most likely cause is a lack of a reliable internet connection or an interruption in the upload process. Having sufficient iCloud storage space alone does not upload content automatically; the iPhone must also be connected to the internet so it can transfer the files to iCloud.

To ensure your videos are uploaded, verify that iCloud Photos is enabled on your iPhone. When iCloud Photos is turned on, photos and videos stored on the device are automatically uploaded and synced with iCloud whenever the iPhone has an active internet connection and sufficient battery power. Once connectivity is restored, the upload process should resume automatically without requiring you to manually transfer the videos.

Regarding your Mac, the Image Capture application serves a different purpose. Image Capture is designed to import photos and videos directly from connected devices such as an iPhone, iPad, digital camera, or scanner and save them locally on the Mac. It does not upload imported items to iCloud, nor does it manage iCloud synchronization. If your goal is to have the videos stored in iCloud, the upload must occur through iCloud Photos on the iPhone or through the Photos app on the Mac with iCloud Photos enabled.

One additional point: 4K videos can be very large files, so uploads may take considerable time, especially on slower Wi-Fi connections. During the upload process, the Photos app may display messages such as “Uploading” or “Syncing with iCloud Photos.”

Image Capture itself does not upload anything to iCloud. Its purpose is to copy (import) photos and videos from an iPhone, iPad, camera, or scanner to your Mac. Image Capture User Guide for Mac

However, there is an important distinction:

1. If you import a video with Image Capture into a folder on your Mac, the video is only stored locally on the Mac.
2. If you then add that video to the Mac’s Photos app and iCloud Photos is enabled on the Mac, the Photos app can upload the video to iCloud.
3. Alternatively, if the imported file is saved in a folder on your Mac that is synchronized with iCloud Drive—such as a folder within iCloud Drive in Finder—the file can be uploaded to iCloud Drive automatically. However, this is different from uploading the file to iCloud Photos, as it will be stored in iCloud Drive rather than in your Photos library.

Image Capture is not an iCloud upload tool. It only imports files to the Mac. Any subsequent upload to iCloud must be performed by another service, such as iCloud Photos or iCloud Drive.

Compress the video so I can send it through Gmail.

The video is already compressed, you might be able to compress it slightly more but not by much. Most email providers will let you send files in the 5 to 10 megabyte range, there is absolutely no way you're going to compress a 30 gig file down to 10 megabytes.

You could try to use an online file sharing program such as Dropbox or share it through iCloud once you have figured out how to upload it.