Heavy buffering on Chrome on remote client

[Xiandros_]

I'm in a long distance relationship (I live in Italy and my GF lives in Serbia) and one way we spend time "together" is by watching movies.
I setup a jellyfin server hosted on my PC and I'm sharing it with her via DUCKDNS and Caddy and she connects via Google Chrome on a laptop.

All the files I download are 4k (I have a 4k monitor), we had no issues with smaller HEVC files while she got very heavy buffering with big REMUX HEVC files to the point where it's unwatchable at every quality setting.

My files are stored on an external HDD and encoding/decoding was left to software.

I'm getting a Samsung T7 SSD today (for unrelated reasons) so I'll move the libraries there. I followed a guide on the Jellyfin site and switched to AMD AMF hardware encoding and decoding, should that fix the issue? Should I leave "enable hardware encoding" and "allow encoding in HEVC format" on?

I'm a complete noob so I'm trying what seems logical

My PC specs:
Windows 10 64bit
AMD Ryzen 7 5800X3D
AMD Radeon 7900XTX
32gb ddr4 ram

Internet speed: 60 Mb/s down, 20 Mb/s up (she has the same download speed)