Unable to upload MP4 videos to Icloud Photos (videos from Google Pixel 3XL)

Hello All

I have just converted as a long time Android user to Apple. All is well EXCEPT uploading my videos to Iclod photos. I have tried the client from the Windows store and the one from Apple direct and both have the same issue - just sticks at uploading XXX number of videos but the upload just does not happen. Photos are OK. The videos are from Google photos downloaded to my PC, they are MP4 and work fine on the PC itself. I managed to copy 44 tiny videos onto Icloud Photos and then anything ovcer 2Mb just never arrives. I purchased 200GB of storage and the actual videos upload to Icloud Drive OK and when you redownload them to the PC they play fine locally. I have tried the usual Apple advised things to try - ticks in boxes, logout/login, reboot etc but nothing works.Its almost like there is a software fault or somesort of conversion issue. I see others have had similar issues but dont seem to have got a fix. Any help would be greatly appreciated - its bery frustrating.