What do you suggest to use for wired connection, if I want to use impala for wireless connection?

[Aster89]

Say I have a system that is normally connected to internet via ethernet, but that sometimes needs to connect via WiFi (possibly leveraging a smartphone used as an hotspot while there's a power outage).

I would like to use impala, so I think I have to use iwd (rather than, say, connaman), but how would I deal with the wired connection?

In short: if I want to use iwd+impala for WiFi, what can I pair to it or also dealing with Ethernet?

[Nexion]

iwd is a wireless connection daemon.
connman by default expects wpa_supplicant, which is another wireless connection daemon. Some people mention that it's possible to make connman use iwd instead:
https://wiki.archlinux.org/title/Talk:ConnMan#connman_+_iwd_as_backend
If it's a working solution for you, then you can use impala to manage wireless connection settings and whatever connman frontend you prefer to manage the rest.

That being said, most common Linux desktop distros with Gnome/KDE use NetworkManager, not connman. Unless you specifically want some connman functionality, you might not have to use it at all. If you want something lightweight on a systemd distro you can instead switch to using systemd-networkd and configure it to prioritize routing via ethernet when it's available. Or on non-systemd distros you can configure ethernet to just use DHCP and write some custom script to monitor ethernet connection status and toggle the wireless interface link state accordingly. The implementation depends on what you are running.