Help with networking

Hello, first post here because i need some help/advice.

I made myself a home server with proxmox and some containers. I have installed Nextcloud, Immich and ownCloud Infinite Scale (along with other things). I bought a Cloudflare DNS and have setup a NGINX reverse proxy from an url from a domain i bought to my public router ip (I exited CG-NAT). I port forwarded the 443 and 80 ports to NGINX and in NGINX i have setup a proxy to my local nextcloud ip and OCIS.

I tried uploading to OCIS and Nextcloud away from home but the internet speed is just bad. Even better, in my house, literally within 1 meter of my server, if i use the dns url i get bad upload speed (havent tried download speed but i guess it's the same). If i use the local url i get normal upload speeds.

Local ip DNS ip
Home 60~70MB/s upload /dwn no test 10~15MB/s upload / download not tested
Away 0 10~15MB/s upload / download not tested

the data is an aproximate, i don't remember the exact data but in the morning i will. I test the speeds with a laptop with wifi (~700Mbs down and ~600Mbs down with wifi one wall away from the router, i don't have another ethernet cable but i am waiting for some to arrive, i gave my last one to my girlfriend)

I have Gigabit internet with fiber, DIGI in Spain with an ZTE H3600P router, a second hand built from scratch server (16GB ram ddr4, msi b450 gaming plus max, AMD radeon pro 2400G, 240GB ssd and 2tb hdd)

The Nextcloud is installed without docker in a container and the nginx is installed with the helper script in another container

I did a iperf3 test locally and it showed fast speeds (i will upload them tomorrow to do them again)

To be honest, i used AI and some youtube tutorials to make some settings and to set it up but i just can't anymore, the AI it's just dumb and i'm tired of it so i call for the help of others (kindly). I tried to make and verify everything it said and to make sure it works but i just don't know how to fix this or if its noral.

The cloudflare dns record is not proxied (gray cloud), the server is plugged in with a capable ethernet cable (900 up 800 down), the containers have DHCP assigned ips by me.

The AI suggested it's something to do with Hairpin NAT or something but i'm too tired of this server and need some real help and advices.

Sorry for the text and every help is much apreciated!

I will provide any extra info if needed