This has been a pain point for a lot of folks and the Memberships team is definitely aware of it, but it’s not a userflow available at the moment.
If you dig back into your invitation email for Memberships there should be an invite to their Beta community where you can track any updates for this. If you can’t find it, just email Webflow support and they can get you one.
I’m not sure about the ecommerce version of Memberships, but I can say with the non-ecomm version that Webflow is manually adding a redirect url param, in the url for us. I’ve been able to hijack that and redirect folks where I want them. Not sure if you’d be able to do that on the ecommerce side, but that’s about my only thought.