I have a NAS with Unraid. I installed nextcloud and averything is working fine (local) the NAS is very fast but when I installed Duckdns and lets encrypt the “online” part is very slow. I have a syncrinasition set up but it is only sync with 1 Mbit/s (large files) (The sync is setup over the Duckdns adress) (the Sync is much faster if I set it up local, but I need it online) The Hardware is not the, limit the CPU is runnung a max 5% (see spec), also my Internet connection schould not be the Limit (down 250 Mbit/s; up 50 Mbit/s)
Nextcloud version: 16.0.3
Operating system and version: UNRAID 6.7.2
It sounds that you want to sync over the internet, where the performance is mostly influenced by the speed of your internet connection. A normal 16 Mbit/s DSL connection is an asynchronous connection with e.g. 16 Mbit/s download and 2 Mbit/s upload speed. Therefore the access speed over the internet is usually slow compared to a LAN connect.
So what kind of internet connection ae you using in detail (upload/download speed)?