How to make sure a video file can be stored in the Photos app? (iPhone)

I would like to offer a video of our festival promotion towards our fans to be then shared on social media. However it seems impossible to offer it in a way that the video can be stored to the Photos app (which would be beneficial since Instagram and TikTok are sourcing the Photos to be shared from there). Is there any way of changing the file format or setting up a certain type of hosting to achieve this? An example file would be: https://family.tapefabrik.de/tomHengst.mp4 I tried converting it to an mp4 file, which did not work.