Are you using a reverse proxy? I use SWAG and I had the same issue (but at a 2GB limit) until I updated nextcloud.subdomain.conf changing:
# proxy_max_temp_file_size 2048m; # Default
proxy_max_temp_file_size 0;
If you're using the NGINX proxy manager you may want to read this. It mentions a similar issue that was resolved by changing the same parameter:
https://www.reddit.com/r/NextCloud/comments/li7fvh/big_files_download_problem/