Virtual Chassis feature support on QFX5120-48YM switch.

• Starting in Junos OS Release 23.1R1, you can interconnect four QFX5120-48YM switches into a Virtual Chassis.
• By default, QFX5120-48YM switches come up in HiGig mode.
• QFX5120-48YM switch model supports only HGoE protocol for virtual chassis formation.
• Only eight 40-Gigabit Ethernet QSFP+ or 100-Gigabit Ethernet QSFP28 front panel uplink ports (ports 48 through 55) can be configured into VCPs to form a QFX5120-48YM Virtual Chassis. Any ports other than those specified above for QFX5120-48YM switches are not supported as VCPs.

https://www.juniper.net/content/dam/www/assets/datasheets/us/en/switches/qfx5120-ethernet-switch-datasheet.pdf

HiGig and HGoE Mode Support for Virtual Chassis: