As far as I know, there has never been an import function, which I always thought was weird. I think the HTML file is just supposed to help you see what changes you've made to your shortcuts so you can copy them in a new version manually.
Either way, you can find your custom keyboard shorcuts XML file by turning on your OS's hidden files and going here...
C > Users > your user name > AppData (normally hidden) > Roaming > Adobe > Dremweaver (your version) > your language > Configuration > Menus > Custom Sets > your custom filename.xml
Once you copy that over to the same location on the second machine, you would need to activate it in the Keyboard Shortcuts dialogue screen by going to Edit > Keyboard Shortcuts > select the shortcuts file in the Current Set dropdown .
Be careful though, I'm not sure what would happen if you brought over custom shortcuts from a much older version with different menu structures, say from CS6 Cloud to CC2021. That might cause issues.