I have now finally got FileMaker Go 19 running on the M1 MacBook as follows:
Download iMazing (free trial)
Click on ‘Manage Apps’
Click on ‘Library’ and download FileMaker Go 19 (enter your iCloud details when prompted)
Once downloaded, right click on FileMaker Go 19 and select ‘Export.IPA’ (I saved to the Downloads folder)
Double click the ‘FileMaker Go 19.1.3.ipa’ file and the IOS installer will add this to the Applications folder, which can be launched as usual.
I had a problem with the above and also, there is something to be very wary of:
After many attempts, I still could not get FM Go to launch. I was getting the following errors:
Nov 25 10:06:34 Andys-MacBook-Pro com.apple.xpc.launchd: Coalition Cache Hit: application<com.filemaker.go.v19(501)> 
Nov 25 10:06:34 Andys-MacBook-Pro com.apple.xpc.launchd (application.com.filemaker.go.v19): FairPlay decryption failed on binary.
Nov 25 10:06:35 Andys-MacBook-Pro com.apple.xpc.launchd: Coalition Cache Hit: application<com.filemaker.go.v19(501)> 
Nov 25 10:06:35 Andys-MacBook-Pro com.apple.xpc.launchd (application.com.filemaker.go.v19): FairPlay decryption failed on binary.
Nov 25 10:06:39 Andys-MacBook-Pro com.apple.xpc.launchd (com.apple.mdworker.shared.0A000000-0500-0000-0000-000000000000): Service exited due to SIGKILL | sent by mds
As a final attempt, I downloaded another small IOS app from a small vendor, which installed and launched without problem. Having done this, FileMaker Go has launched consistently since. I can’t explain why, but it worked.
Finally a warning, which I only spotted after a FileMaker Developers Zoom session last night. I had decided to use FM Go to run my reference database, timesheet, customer, tech info, etc. but when I opened the file it disappeared from its folder.
FileMaker Go moves, not copies, the file from its location to ~Library/Containers/FileMaker Go 19/Data/Documents in this case. This Data folder contains some shortcuts to Desktop, Downloads then some other dedicated folders as per the attached screenshot. I won’t be using FM Go on my Mac until I get a better understanding of this, as I share the file frequently with my iPhone and iPad Pro’s.
The software runs very much like it does on the iPad, with the familiar buttons and menus.