Unable to search the people from keycloak OIDC

### Description

We are running synapse local and we configure keycloak OIDC & we have 1000 users, but we are unable to see them until they login in atleast once in syanpse.

### Steps to reproduce

- Run synapse server and client
- configure OIDC.
- login in element search for the people

### Homeserver

chat-server.intellaire.com

### Synapse Version

{"server":{"name":"Synapse","version":"1.86.0rc2"}}

### Installation Method

Docker (matrixdotorg/synapse)

### Database

PostgreSQL

### Workers

Single process

### Platform

VM Ubuntu

### Configuration

_No response_

### Relevant log output

```shell
2024-04-26 10:08:36,785 - synapse.rest.client.sync - 231 - INFO - GET-2099 - Client has disconnected; not serializing response.
2024-04-26 10:08:36,785 - synapse.http.server - 782 - WARNING - GET-2099 - Not sending response to request , already disconnected.
2024-04-26 10:08:36,786 - synapse.access.http.8008 - 473 - INFO - GET-2099 - 10.80.16.118 - 8008 - {@naresh.m:chat-server.intellaire.com} Processed request: 30.003sec/-10.704sec (0.000sec, 0.000sec) (0.000sec/0.001sec/2) 0B 200! "GET /_matrix/client/r0/sync?filter=0&timeout=30000&since=s35_285_0_21_50_1_7_30_0_1 HTTP/1.0" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/123.0.0.0 Safari/537.36" [0 dbevts]
```

### Anything else that would be useful to know?

_No response_