Moving mp4 videos from PC to icloud photos (and photos app on iphone), how to and size limit?

Thanks in advance for any help on this.

It seems using icould in a browser only allows photos to be uploaded to my icloud photos, no video. I did figure out I can upload the videos to icloud drive, play them on my iphone, and then save SOME to my photos using the send arrow while watching the video. However, it seems videos over a certain size or length I cant save them to my photos. I was able to save a file 1.05G (4:58 long) but not anything bigger.

Is there a limit to file sizes, a work around for it, or a better way to transfer these files? Thanks