Manage all overrides from a a single domain like before

Thanks for the report, hanoii. This is an intentional change in 3.x rather than a bug, so let me explain the new model and what it means for your workflow.

In 2.x, Domain Config UI added a domain/language selector to admin forms (the old SwitchForm, backed by the session). You stayed on one domain and chose which domain to write the override to.

In 3.x the module was rebuilt on top of per-domain config collections (see #3060758), and domain negotiation now runs early in the request. As a result, configuration overrides always apply to the active (negotiated) domain — the one whose hostname you are currently browsing. The in-form selector was removed because the target domain is now determined by where you are, not by a dropdown.

So the new workflow to manage a domain's overrides is:

• Browse to that domain using its own hostname.
• Open the admin form, enable domain configuration if needed, edit, and save — the value is stored for that domain.
• To edit another domain, browse to its hostname and repeat. As you noted, the same administrator credentials work across all domains.

To make moving between domains painless, you can use the domain_sso module from the Domain Extras project. It provides single sign-on across your domains, so once you are logged in on one domain you are authenticated on the others — you can hop from one domain's admin form to another's without re-logging in each time.

I appreciate that centralizing everything on the main domain was convenient, and I understand the regression in convenience. Re-introducing an optional admin-side selector on top of config collections is possible (for example, letting an admin temporarily target another domain's collection without switching hostname), but it has to be reconciled with negotiation, cache contexts, and per-domain access — so it is better tracked as a separate feature request than as part of this support issue. If you would like that, I am happy to open one and link it here.

I will correct the module README, whose example still describe the removed selector.

Good news, @hanoii: a dedicated submodule to bring this workflow back is now in progress. Domain Configuration Switcher (tracked in domain_extras #3592820) adds an in-form domain selector so an administrator can configure any domain from a single host, without logging in to each domain -- which is what you asked for here.

It is built on a small config-editing seam in domain_config_ui (#3592832) and is verified to work on sites using language path prefixes and path-prefix domain mode.

Config translation is not yet retargeted by the switcher (a documented follow-up).

Feedback welcome on #3592820.

Closing as "Won't fix" (in core Domain module) for now.