For pxco operator version 1.11 (branch release-1.11.0) and pmm version 2.28, pmm-client can't connect to pmm-server using password. 
I works fine if we use api key or 1.10 operator version with pmm 2.28. 
STR:
0.  Add password to secrets 

pmmserver: admin

1. Deploy secrets with deploy/secrets.yml
2. Deploy pmm-server
3. Deploy bundle
4. Deploy cr.yaml 
in cluster1-pxc-0 logs we can see 

INFO[2022-05-30T13:43:22.562+00:00] Updating PMM Server address from "monitoring-service" to "monitoring-service:443". component=setup
pmm-agent is running.
Registering pmm-agent on PMM Server...
Failed to register pmm-agent on PMM Server: invalid username or password
Please check username and password.
[u'pmm-agent', u'setup'] exited with 1.
Restarting [u'pmm-agent', u'setup'] in 5 seconds because PMM_AGENT_SIDECAR is enabled ...
Starting [u'pmm-agent', u'setup'] ...
INFO[2022-05-30T13:43:27.598+00:00] Loading configuration file /usr/local/percona/pmm2/config/pmm-agent.yaml. component=setup
INFO[2022-05-30T13:43:27.598+00:00] Using /usr/local/percona/pmm2/exporters/node_exporter component=setup
INFO[2022-05-30T13:43:27.598+00:00] Using /usr/local/percona/pmm2/exporters/mysqld_exporter component=setup
INFO[2022-05-30T13:43:27.598+00:00] Using /usr/local/percona/pmm2/exporters/mongodb_exporter component=setup