I thought I was the only one!
At first, I noticed I could only log in on three devices — I figured Disney had quietly changed their policy.
Then tonight, when I tried to stream Moana 2, I realized I was also limited to 1080p. Apparently, 4K streaming now requires an upgrade.
I’m on the same 1Gb Pro upgrade too, so this really came out of nowhere.

are u by chance using wifi?

because unless ur wifi (wifi 6e or 7 with 1 Gbps or better throughput over wifi) is good, i wouldnt be surprised if u not get the full 1Gbps dl speed.

If u r using wired this is less likely to be the issue, and probably something else.
https://dongknows.com/wi-fi-range-expectations-vs-reality/
if ur using wifi, check the reviews what thoroughput u can expect from it. also try test using wired see if ur broadband improve. use a speed test website to check ur speed.

if ur testing wifi only, use a self hosted app like speedtest to see if wifi is ur issue.
for myself i am only using 100 mbps /50 mbps. already tested no issue. but the higher u go, the more bottlenecks u run across. its figuring which it is. ur wifi? the isp? bad ethernet cables? or something else.