I tried that as well. I've now tested trainers for Divinity Original Sin 2, No Man's Sky, and Terraria with no problems. I only have this problem with Hollow Knight trainer. I have tried activating it via the .exe and via the trainer manager. Both option bring up the "Customized For ~~~" which then disapears as normal but instead of bringing up the trainer it brings up a dialogue to chose a program to run .tmp files. It does not do this for the other game trainers, only for Hollow Knight. I have set all windows apps to default and it still wont open. After following all steps provided by this site this still remains the only trainer that will not open/function. I am able to open COSMOS but figuring out how to find the correct values is a pain and I've only been able to figure out insta-kill. So basically, all other trainers work, COSMOS works, and none of the guides or recommended fixes make the Hollow Knight trainer work. I cannot replicate the error/issue with any other trainer.
If you would like we can setup a TeamViewer session to do hands-on troubleshooting directly on your PC. Please open a support ticket if this is something you would be interested in. www.cheathappens.com/support.asp
How to clean previous stored trainer data. Delete the folders listed or make your own batch file to clean them for you.
Or manually delete all files in