This is a shared, but not external router (so no NAT-ing). We allocate public v4/v6 to instance from it.
Actually, we use it, as a "VPS" network (it's a network of admin user anyway)

So, we have routers here, because we use v4 DHCP and metadata from it.

To be more specific:
[PROD][root(cc1:0)] <~> openstack network show Flat1
+---------------------------+----------------------------------------------------------------------------+
| Field                     | Value                                                                      |
+---------------------------+----------------------------------------------------------------------------+
| admin_state_up            | UP                                                                         |
| availability_zone_hints   |                                                                            |
| availability_zones        | nova                                                                       |
| created_at                | 2020-07-01T22:59:47Z                                                       |
| description               |                                                                            |
| dns_domain                | None                                                                       |
| id                        | fa55bfc7-ab42-4d97-987e-645cca7a0601                                       |
| ipv4_address_scope        | None                                                                       |
| ipv6_address_scope        | None                                                                       |
| is_default                | None                                                                       |
| is_vlan_transparent       | None                                                                       |
| mtu                       | 1500                                                                       |
| name                      | Flat1                                                                      |
| port_security_enabled     | True                                                                       |
| project_id                | b48a9319a66e45f3b04cc8bb70e3113c                                           |
| provider:network_type     | vlan                                                                       |
| provider:physical_network | vltrunk                                                                    |
| provider:segmentation_id  | 719                                                                        |
| qos_policy_id             | None                                                                       |
| revision_number           | 3                                                                          |
| router:external           | Internal                                                                   |
| segments                  | None                                                                       |
| shared                    | True                                                                       |
| status                    | ACTIVE                                                                     |
| subnets                   | 84b83375-85a3-4b8a-8656-50eec8fccc2e, a5a9991c-62f3-4f46-b1ef-e293dc0fb781 |
| tags                      |                                                                            |
| updated_at                | 2020-07-01T22:59:53Z                                                       |
+---------------------------+----------------------------------------------------------------------------+

for metadata, we use the qrouter based one, with static route on IPv4:

[PROD][root(cc1:0)] <~> openstack subnet show Flat1-subnet-v4
+-------------------+-------------------------------------------------------------+
| Field             | Value                                                       |
+-------------------+-------------------------------------------------------------+
| allocation_pools  | 193.224.218.1-193.224.218.250                               |
| cidr              | 193.224.218.0/24                                            |
| created_at        | 2020-07-01T22:59:50Z                                        |
| description       |                                                             |
| dns_nameservers   | 193.224.161.70, 193.224.161.86                              |
| enable_dhcp       | True                                                        |
| gateway_ip        | 193.224.218.254                                             |
| host_routes       | destination='169.254.169.254/32', gateway='193.224.218.251' |
| id                | 84b83375-85a3-4b8a-8656-50eec8fccc2e                        |
| ip_version        | 4                                                           |
| ipv6_address_mode | None                                                        |
| ipv6_ra_mode      | None                                                        |
| name              | Flat1-subnet-v4                                             |
| network_id        | fa55bfc7-ab42-4d97-987e-645cca7a0601                        |
| project_id        | b48a9319a66e45f3b04cc8bb70e3113c                            |
| revision_number   | 0                                                           |
| segment_id        | None                                                        |
| service_types     |                                                             |
| subnetpool_id     | None                                                        |
| tags              |                                                             |
| updated_at        | 2020-07-01T22:59:50Z                                        |
+-------------------+-------------------------------------------------------------+

(don't be confused about the "Flat" naming.. it's a VLAN based network, it's just the name)

Regards:
 Peter