I just upgraded to a new iMac with High Sierra OS. My FMP Advanced seems to still work, but am I headed for grief?
As other have alluded to - FileMaker Pro 14 has not been tested / certified to work with High Sierra. There could be some unknown pitfalls or compatibility issues out there. I'd be leery about running an app that was tested up to macOS 10.11 - especially an app that stored my precious data in it.
In other words, you are swimming without a lifeguard on this one.
Search on the Community, my guess is that the answer has already been given.
As advised by planteg, you could search for issues involving High Sierra and see what you come up with. However, if it is working it is working, so press on.
For the record, here is the link to version history:
Retrieving data ...