Hello

According to the Dell EMC S5248F-ON switch documentation, the switch supports multi-rate 100GbE ports that can operate at 10/25/40/50/100GbE

This means you can use a 40GbE QSFP+ module in a 100GbE QSFP28 port, but the performance will be limited to 40GbE.

For detailed configuration steps and compatibility checks, you can refer to the Dell EMC S5248F-ON documentation