Forced Login & SEO

Sorry, I am still a bit of a noob at these kinds of things.

I have spent a lot of time building SEO recently, but then realized I needed to use a forced login, which redirects to the login/register page upon attempting to access the website.

Does this hurt SEO in any way? My answer is probably yes, but I just needed to be sure/confirm.

If your website won't be available publicly, that means that google crawlers won't be able to crawl it and the pages won't get indexed, so you simply won't get any SEO organic traffic using this method