If both ports allow autonegotiate and support 100mb over copper then there should be no problem. they should negotiate to 100mb, if the gig port is gig only then you will not be able to interconnect with a 100mb port.
I recommend setting to auto-negotiate unless there is some prefailing reason not to. I have had issues with port disabling themselves we 10/100/1000 server NICs or plugged into Cisco 10/100 modules. If auto-negotiate is enabled you will be able to review logs to determine any issues. If you enable non-negotiate you will not get any definitive port error logs.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...