I finally fixed it. And the solution was really stupid. I had tried to find help on the virt-manger command but for some reason didn’t think of googling for the man page. I finally did this morning and found out here that virt-manager --debug exists:
$ virt-manager --debug
[Tue, 30 Aug 2022 10:55:47 virt-manager 32322] DEBUG (cli:204) Version 4.1.0 launched with command line: /usr/bin/virt-manager --debug
[Tue, 30 Aug 2022 10:55:47 virt-manager 32322] DEBUG (virtmanager:167) virt-manager version: 4.1.0
[Tue, 30 Aug 2022 10:55:47 virt-manager 32322] DEBUG (virtmanager:168) virtManager import: /usr/share/virt-manager/virtManager
[Tue, 30 Aug 2022 10:55:47 virt-manager 32322] DEBUG (virtmanager:205) PyGObject version: 3.42.2
[Tue, 30 Aug 2022 10:55:47 virt-manager 32322] DEBUG (virtmanager:209) GTK version: 3.24.34
[Tue, 30 Aug 2022 10:55:47 virt-manager 32322] DEBUG (systray:476) Showing systray: False
[Tue, 30 Aug 2022 10:55:47 virt-manager 32322] DEBUG (inspection:203) python guestfs is installed
[Tue, 30 Aug 2022 10:55:47 virt-manager 32322] DEBUG (inspection:225) libguestfs gsetting enabled=False
[Tue, 30 Aug 2022 10:55:47 virt-manager 32322] DEBUG (engine:113) Loading stored URIs:
qemu:///system
[Tue, 30 Aug 2022 10:55:47 virt-manager 32322] DEBUG (engine:461) processing cli command uri= show_window=manager domain=
[Tue, 30 Aug 2022 10:55:47 virt-manager 32322] DEBUG (engine:464) No cli action requested, launching default window
(virt-manager:32322): Gtk-WARNING **: 10:55:47.629: Could not load a pixbuf from icon theme.
This may indicate that pixbuf loaders or the mime database could not be found.
**
Gtk:ERROR:../gtk/gtk/gtkiconhelper.c:494:ensure_surface_for_gicon: assertion failed (error == NULL): Failed to load /home/johannes/.local/share/icons/Tela-dark/24/actions/image-missing.svg: Error opening file /home/johannes/.local/share/icons/Tela-dark/24/actions/image-missing.svg: No such file or directory (g-io-error-quark, 1)
Bail out! Gtk:ERROR:../gtk/gtk/gtkiconhelper.c:494:ensure_surface_for_gicon: assertion failed (error == NULL): Failed to load /home/johannes/.local/share/icons/Tela-dark/24/actions/image-missing.svg: Error opening file /home/johannes/.local/share/icons/Tela-dark/24/actions/image-missing.svg: No such file or directory (g-io-error-quark, 1)
Aborted (core dumped)
Wait, so the problem is missing Icons??? Yes, even changing the icon theme to Tela green dark fixes the issue 
.