I have an application where I set up a Juniper EX-2300 as a layer 3 switch – but I needed DHCP Relay activated through the EX-2300

edit forwarding-options
# enter your dhcp server(s)
set dhcp-relay server-group DHCPSERVERS 10.9.6.254
# mark them active
set dhcp-relay active-server-group DHCPSERVERS
# group the interfaces that have clients that need dhcp addresses
set dhcp-relay group DHCPCLIENTS interface irb.90

In my application, the client machines that need ip addresses are connected via irb.90

tested with version 21.3R1.9 on a ex2300-c-12t