How can you keep a count of the number of times your uploads have been downloaded by others?

You would either have to find a hosting service that captures such information, or use a link protection service that does. For example, I looked at my Mega account and do not see this info. However, the link protection service called IsraClick can at least tell you how many times a link has been viewed (regardless of whether it was downloaded or not). Here's an example of such a link: https://isra.click/181israbox_Finding%20Shore. You need to be aware that some of these views might be by internet crawlers and robots (like Google).

thanks for the info, I'll investigate that,