Just say it in a general way.
Most videos are either in Mp4 or MKV format. Those two are just "containers" of a video file. Because inside the file there are multiple tracks: video track, audio track, subtitle track, chapters info ... etc.
The video track usually use either H264(aka AVC1) or H265(aka HEVC) as the compression method. Insta360 files should be in 264 format, and their size should be big, like 1GB for each minute. However, that's not really big if you ever see the size of an uncompressed video file.
So to upload the video, you need to choose the right file, the one that ends with Mp4 or MKV, not the other format. And your web browser should be an updated one, not the ancient Internet Explorer. Then you should be able to upload the whole thing.