Let’s try this a different way:
- Post your config as requested in the support template
- i.e. output of occ config:list system - Set your log level to something reasonable for now (2 is the default; 0 is way too noisy unless we really end up in the weeds troubleshooting something).
- See what log entries pop up in your Nextcloud log while reproducing the problem
The 403 Forbidden is coming from somewhere. The transaction is being blocked server-side for something likely related to a forbidden filename, anti-virus scanner, or any number of other ways to block files/connections.
Ideally also check your web server error log, since it’s possible something else weird is going on such as filtering at your web server level outside of Nextcloud.