Almost.

It looks like when we added support for the old Netscape ".html" files, we neglected to add it to the list of supported file types for AppleScript.  You can export it as a ".xbel" file, which is similar to, but not html.

Another issue is that Synkmark will import from whatever browsers are listed in Preferences > Syncing.

The following AppleScript will import from the listed browsers and export to a file on the Desktop.

tell application "Synkmark"
     tell collection 1 to import
     export only collection 1 file format Xbel path "/Users/jk/Desktop/My-Bookmarks.xbel"
end tell

We could certainly fix the omission of "html" in a future version.

Also, although we are deep into reverse-engineering macOS 13 and don't have the time to look at it now, I think that our more advanced app BookMacster might be able to do this more readily.  You might make two .bmco collections, one configured to import Safari and export to your .html file, the other to import Chrome and export to your .html file, then in Syncing > Advanced, set up a Scheduled operation to do the Import followed by Export.

If you can't get this to work, contact us after we've published version 3 of our apps, maybe next week/month.