Have to tell you that there is probably no solution for nextcloud speed problems, there is no difference is that iOS or NC windows app.
I have wasted tens and tens of hours for debugging it over past 2 years. It has to be related docker, unraid docker network or specifically to this NC container. There are main 2 suspects on this case, for some reason php-fpm takes alot of time to process files that are uploaded ( 10mb chunks) and/or there is some specific internal docker network problem why it takes so long to transfer that file.
Another server with much less cpu and ram and there i can upload 500-800mbit/s (server is 700 km away from my home, without docker, it uses reverse proxy also). On that server it takes about 400-800ms to process one chunk(10mb), compare with unraid docker NC where it takes 2-3 seconds. 4 core cpu with lower ghz and 6gb ram can process 15 times faster NC on bare metal than dual cpu xeon with 64gb ram on docker.
There is no config file that i have not modified/tuned nginx, php, mysql, memcached, APCu, Redis... you name it
Btw nginx and NC combo loves http1 not http2, there is alot talk about it on github/NC forum. Thats why im using on my second server http1 only, network speed went from 50mbit/s to almost gigabit....
However on my unraid server im out of ideas.