The MX will act as the router and will segregate the broadcast domain when you connect the switch to the MX LAN and hence it will not be able to get an IP from the cable modem. You can enable DHCP on the MX itself under "security & SD-WAN > DHCP".
The default port configuration for the switches is Trunk with native vlan 1 (Unless you change it). I would suggest to configure port 10 on the MX to the same and enable DHCP in vlan 1 and you should be all set. Let us know how it goes.
Cheers!
Raj
If you found this post helpful, please give it kudos. If my answer solved your problem, click "accept as solution" so that others can benefit from it