How much longer does it take for you to open? When opening a module via the command line (which includes opening via the jump list), the module window is created while the splash screen is still shown, and creating that window can take a while. Is the extra time spent on the splash screen approximately comparable to the time it takes to open the module from within OpenMPT, or is it much longer?

I think I found a potential difference when launching a module from the jump list. Essentially OpenMPT was filling the instrument browser with the contents of the current working directory, which ends up being the System32 folder when launching from the jump list, and that folder contains a lot of files. Can you check if r14619 works better for you? It will be available in an hour or two from https://builds.openmpt.org/builds/auto/openmpt/pkg.win/1.30/

I think r14619 is a little better, but still slow - 5 seconds on splash screen.
After I changed the default path for instruments to another directory the problem disappears completely.
So I guess you are definitely on the right track.

Ah yes, if you previously didn't set an instrument directory at all, it would still fall back to using the current working directory. I think r14621 should work for you even when there is no instrument directory set up.

yes. now it works super fast with default settings. thank you!

Great. :)