Hey there triciach4,
Thanks for reaching out to the Apple Support Communities today.
To get started, based on the information you've provided the videos would be within the time limit to add to a shared album; however, have you ensured that the video is in a supported format? We ask because only H.264 and MPEG-4 file formats can be added to a shared album. You can find this information listed here: Shared Album limits - Apple Support
Supported file types for Shared Albums
Shared Albums upload a copy of your data. Downloaded content may not contain the same information as the original.
* Image formats: HEIF, JPEG, RAW*, PNG, GIF, TIFF
* Video file types and formats: HEVC, MP4, QuickTime, H.264, MPEG-4
Shared Albums also support special formats that you capture with your iPhone, like slo-mo, time-lapse, Live Photos, and Memory videos. When shared, photos are reduced to 2048 pixels on the long edge, except panoramic photos, which can be up to 5400 pixels wide. You can share GIFs that are 100MB or smaller.
Videos can be up to fifteen minutes in length and are delivered at up to 720p resolution.
To check the video format, just open the video in the Photos app on your iPhone, and tap the Information button (i). If you've confirmed that the videos are in a supported format, try restarting your iPhone with the steps in this next link here: Restart your iPhone - Apple Support
While restarting your iPhone may seem like a simple step, it can often help with resolving some unexpected issues like this.
Keep us updated on the results.
Take care!