I found the issue with some help from their Git. I'm posting it here because it's not well-documented and doesn't seem to be mentioned anywhere else. (EDIT: Hats off to the dev, who upon seeing my Git post went and updated the documentation to specifically recommend reviewing this directive!)
Peertube DOES throttle network speed! A fresh install is limited to 5 MB/s. This is fine for 1080P but barely adequate for typical 30 FPS 4K footage, and unworkable for high-quality 4K or 4K at 60 FPS. For perspective, YouTube recommends nearly 9 MB/s for 60FPS 4K video.
You can adjust this hard limit by modifying peertube.conf and adjusting the values listed below:
proxy_limit_rate
$peertube_limit_rate
You should take your network performance, desired video quality, and download functionality into consideration before modifying these. For most people, 10M should give you ample 4K quality without excessive buffering. If you want to allow downloads, consider setting them to 25M or higher.
I'm glad this wasn't a Cloudron issue, but I appreciate the effort of anyone who took the time to stop and think about this one. I suspect this value was different in previous versions and carries over with upgrades; this may only affect new installations.
