Windows 10 has its own free video editor but I found another one which I used/preferred - however I'm not at home for a few weeks to look and see what I installed and I can't recall the name of it. It may well have been Videopad www.nchsoftware.com/videopad/
WhatsApp compresses the video to a smaller file size.
If Facebook Messenger says it's too large to be able to send, and the recipient isn't on Facebook Messenger, I send the video to my own WhatsApp profile, then save it back to the photo library on my iPhone. Then send it to them on FB. Bit of a faff I know, but it works.