If you need to just upload a file you can use CloudBerry Explorer - https://www.msp360.com/explorer/windows/amazon-s3.aspx

You can use Simple Backup Mode with CloudBerry Backup as described here. https://help.msp360.com/cloudberry-backup/backup/cloud-to-local/step-5-specify-backup-mode

Thank you Alexander. Can cloudberry explorer be scheduled? I'm looking for auto-backups of a folder every few minutes

Thanks David. This option seems to be only available for cloud>local backups. I want it on the local>cloud backups. Is there a way to enable it there?

if you need to schedule uploads then use Simple Mode in CloudBerry Backup as David suggests. It works for local-to-cloud backups too. Just pick "Files" and then "Simple Mode" on step 4 of the Backup Wizard. If you're running version 7.2 or higher, make sure to select "Files Backup (Legacy)" from the drop-down (see GIF below)

I can't see an option for "simple mode". Is it because I'm using the free version?

please ignore my last comment. I saw the GIF you posted and it seems I got it right. I was tying the "files backup" not the "files backup (legacy)" option.

The legacy option has the simple mode as you mentioned. Thanks.

On a side note, why is the simple mode only in the legacy option? Will it disappear in a future version?

As you noticed the new backup format uses a proprietary format to process and store backups, which makes Simple Mode impossible in this implementation. We don't plan to discontinue the "legacy" format any time soon.

Thanks Alexander.
As a suggestion, you might want to change the word "legacy" as it might raise concerns for people needing the "simple mode".
Thanks for all the support in this thread.