Unfortunately your only real options are wait until it launches or don’t show it. Employers will take into account there is work you can’t show, but if you’ve been at a job for several years and have nothing to show, your best bet is to wait until that project launches or do something on the side that demonstrates what you’re good at.
You can always talk to what you’re doing currently, but as they say “talk is cheap”.
Avoid ever trying to “Sneak a peek” since the design community is extremely small. You’ll never know who you’re presenting to at Company Y might have been college roommates with your boss at Company X and gives them a phone call after seeing your secret project.