welcome,
I have a very similar problem.
softaculous install ispconfig3 it works perfectly.
when ispconfig is the left menu, I click on the autoinstall menu (here within ispconfig3 the installable programs should appear as on the softaculous home page.
but it can't load, only broken images, and template has error 404 error.
e.g:
https://mail.hostingozd.hu:8080/themes/default/bootstrap/css/bootstrap.min.css?5.7.2 net :: ERR_ABORTED 404
I would not copy the rest.
but it does not load.
the / var / softwww / folder exists and is linked to softimages and themes in / usr / local / softaculous / enduser /