I'm the owner of this account, have created a folder for it ("free" Basic), and used the proper Dropbox channel to UL a file to it. Plenty of space available fpr the file. The person the folder is being shared with received their "folder share" notification. The endless loop is a new glitch, and nothing else about my machine has changed.
Mac M1 Air, OS 11.2.8, either Firefox 109.0.1 or Safari 14.1.2