YouTube restored ‘sort by oldest’ option for channels.
In Nov of 2022 YouTube removed the sort by oldest option.
Now, the oldest sort option is back.
YouTube actually announced they would be bringing the oldest sort back in this video from May of 2023.
The reason they gave for removing it was:
Oldest was because it was only supported in a mixed mode when videos, live, and shorts appeared in the same feed.
With the introduction of chips and separated tabs by format, this no longer existed.
They have rebuilt it and released it. So now we can time machine and see the oldest video on a channel with ease.