get the function "sorted by oldest" which youtube has removed
Discussion
for everyone who's asking this, follow me here:

[1] add this extension to your browser(i.e. chrome)

[2] after installation, click that extension button, select "css" panel, and paste this code into it:

#contents.ytd-rich-grid-renderer {
width: 100%;
padding-top: 24px;
display: flex;
flex-wrap: wrap;
justify-content: flex-start;
flex-direction: column-reverse;
}
#contents {
flex-direction: row-reverse;
}
[3] go to any youtube profile's videos page. instead of click the "sorted by oldest" button youtube has removed, you now click that extension. (wait 1~2 seconds here we go. now all videos are sorted by oldest)

[4] so for now, anytime you want to sort, just go to any videos' page, and click the extension button