When adding multiple devices classes to /etc/microshift/lvmd.yaml, only the first is considered. The other one is ignored     

MicroShift Version: 4.14.43    

    always

Ensure there are two volume groups available. In this example, its "rhel" (from the base installation) and "ushift2" on another disk:
# vgs
  VG      #PV #LV #SN Attr   VSize   VFree 
  rhel      1   2   0 wz--n- <63.00g  30.96g
  ushift2   1   0   0 wz--n- <30.00g <30.00g
# pvs
  PV         VG      Fmt  Attr PSize   PFree 
  /dev/sda   ushift2 lvm2 a--  <30.00g <30.00g
  /dev/vda2  rhel    lvm2 a--  <63.00g  30.96

Add the two volume groups as device classes to /etc/micorshift/lvmd.yaml:
# cat /etc/microshift/lvmd.yaml
socket-name: /run/lvmd/lvmd.socket
device-classes:
  - name: default 
    volume-group: rhel
    default: false
    spare-gb: 0
    type: thin
    thin-pool:
      name: thin
      overprovision-ratio: 1
  - name: uhift2 
    volume-group:  ushift2
    default: true
    spare-gb: 0
    type: thin
    thin-pool:
      name: thin
 
Restart Microshift, or reboot the host to be sure.
   

Only one storage class:
# oc get sc
NAME                            PROVISIONER   RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
topolvm-provisioner (default)   topolvm.io    Delete          WaitForFirstConsumer   true                   19h
    

Two storage classes of name "Default" and "Ushift", matching the device classes.    

Per slack discussion, this seem to never have been implmented. But multiple device classes is explicitly stated in the docs as an example: https://docs.redhat.com/en/documentation/red_hat_build_of_microshift/4.17/html/storage/microshift-storage-plugin-overview#microshift-storage-device-classes_microshift-storage-plugin-overview