Proxy: it's also not clear to me what the difference between the "Auto Detect" button there and the "Detect proxy configuration automatically" is.

"Auto Detect" means "look at the system env vars now, and fill the GUI from what they say.
"Detect proxy configuration automatically" means "later, whenever the user opens a connection, run a bit of javascript that will tell us what the proxy is depending on the host we're trying to reach" (the KPAC functionality)

Browser Identification:
Probably mostly relevant for Konqueror. Or is there a use case for changing the user agent for the webdav KIO slave?

Not even webengine-based Konqueror respects that setting and I assume webkit-based doesn't either.

I don't see any use for the "Browser Indentification" KCM and would propose to remove it.

I don't see any use for the "Browser Indentification" KCM and would propose to remove it.

Agreed

https://invent.kde.org/frameworks/kio/-/merge_requests/438

I assume webkit-based doesn't either

That part is incorrect. The webkit-based engine did use KIO. But well, it's dead too.

Regarding "Connection Preferences": even ignoring that it's probably only relevant to KIO, I don't think this stuff should be exposed to regular people (when was the last time *you* changed your timeout values?):

I feel this is something that is best left for config files, so we should hide it at least

We live in a world of fast reliable internet. I suspect people in less-well-equipped ("third world") countries might have a use for increasing timeout values so the system tries longer before giving up. But yes this was more useful when it was about your internet browsing, while now if it's just about your DAV connection....

do programs that use DAV use settings from this KCM though?

Actually forget about DAV, FTP is a better example.

kio_ftp does m_server->waitForNewConnection(q->connectTimeout() * 1000);
and SlaveBase::connectTimeout() reads from kioslaverc, which src/kcms/kio/ksaveioconfig.cpp writes to.

It's the sort of thing that is occasionally useful for some people some of the time somewhere somehow, but mostly useless for 99% of people. Perhaps there is a third option: turn it into an advanced page or a dialog accessed from another KCM. Surfacing this stuff in its current location is super overkill, but maybe we can just hide it better.