An ACX7100 with a 100Gb QSFP:

root@gamora> show chassis hardware detail no-forwarding

Hardware inventory:
Item            Version Part number Serial number    Description
Chassis                             XXXXXXXXXXXX     JNP7100-32C [ACX7100-32C]
PSM 0           REV 04  740-085431  XXXXXXXXXXXX      PSU 1600W AC, Front to Back Airflow
PSM 1           REV 04  740-085431  XXXXXXXXXXXX      PSU 1600W AC, Front to Back Airflow
Routing Engine 0 REV 09  611-112446  XXXXXXXXXXXX     RE-JNP-7100
 sda  100030 MB SFSA100GM2AK4TO-   000060204085FE000002 Solid State Disk
 sdb  100030 MB SFSA100GM2AK4TO-   000060204084950000D8 Solid State Disk
CB 0            REV 15  650-113148  XXXXXXXXXXXX      Control Board
FPC 0                    BUILTIN     BUILTIN          ACX7100-32C
 PIC 0                  BUILTIN     BUILTIN           MRATE- 32xQSFP-DD + 4xQSFP56-DD
<../>
   Xcvr 20     0       NON-JNPR                      QSFP-100GBASE-LR4

Is having an issue with getting link.  The port shows state as Down with a flag set to Transceiver-Absent:

root@gamora> show interfaces extensive no-forwarding
Physical interface: et-0/0/20, Enabled, Physical link is Down
 Interface index: 1053, SNMP ifIndex: 545, Generation: 597000455426
 Link-level type: Ethernet, MTU: 9192, LAN-PHY mode, Speed: 100Gbps, BPDU Error: None, Loop Detect PDU Error: None, Ethernet-Switching Error: None, MAC-REWRITE Error: None, Loopback: Disabled, Source filtering: Disabled, Flow control:    Enabled, Auto-negotiation: Enabled, Media type: Fiber
 Device flags : Present Running Transceiver-Absent
<../>
 Ethernet FEC Mode :                 FEC91
   FEC Codeword size                    528
   FEC Codeword rate                  0.973

The issue is tied to the FEC Mode.  The interface defaults to FEC91.  However, the QSFP28-100G-LR4 does not support any FEC mode in Junos EVO.

For link to come up with the optics, FEC mode should be set to 'none':

root@gamora# set interfaces et-0/0/20 ether-options fec none