As per comment [1], here is a limited list:
```
|----------------+----------------------------------------+-------------+----------------|
| listing status | url | instance | # listed repos |
|----------------+----------------------------------------+-------------+----------------|
| done | https://gitlab.com/api/v4 | gitlab | 964329 |
| done | https://salsa.debian.org/api/v4/ | debian | 23757 |
| done | https://framagit.org/api/v4/ | framagit | 12134 |
| done | https://gitlab.inria.fr/api/v4/ | inria | 1606 |
| done | https://gitlab.gnome.org/api/v4/ | gnome | 3825 |
| done | https://gitlab.freedesktop.org/api/v4/ | freedesktop | 1949 |
| done | https://0xacab.org/api/v4/ | riseup | 883 |
| done | https://gitlab.common-lisp.net/api/v4 | common-lisp | 551 |
| done | https://gite.lirmm.fr/api/v4 | gite.lirmm | 292 |
|----------------+----------------------------------------+-------------+----------------|
```
[1] https://forge.softwareheritage.org/T1111#20926