I have a 20 megabit per second upload speed on my computer running with wifi.
Duplicati runs on my Synology NAS DS220+ through a Docker Container. Duplicati copying data from the NAS to Microsoft OneDrive runs at about 360 kilobytes per second = 2.9 megabits per second.
The rated speed of the NAS drives is 230 MB/s.
Maybe it’s the Celeron CPU on the NAS that’s slow at encryption?
P.S. Speed limiter is disabled
Duplicati isn’t doing just a raw data copy. There is a lot of processing that it does behind the scenes: reading your source data, splitting into chunks, hashing, deduplicating, creating backup archives, compressing, encrypting, and tracking everything in a local sqlite database.
Some of these are single threaded operations and would be affected by slower CPU.
I see you are not doing any speed throttling in Duplicati itself, but is your docker container configured to limit CPU or RAM?