I really think you should be unsubscribing a lot. An inbox full of only things that matter is a good place to be.
But when you’re doing that unsubscribing, what you’re unsubscribing from is junk not spam. Spam, hopefully, is a very small problem for you. Perhaps a few spam emails leak into your inbox a week and you click the button to mark them as spam. Junk is the real problem. Junk is real email that you just don’t care about.
An inbox full of junk is the #1 contributor to email overload that people experience. Their inbox has 2,874 unread emails, because 2,764 of them are junk. That feels like an extraordinary amount of work to come back from. My advice is to chip away at it over time.
What you shouldn’t do is tediously click and delete each one at a time. Just deleting them is a very temporary solution. They’ll be back. Chipping away at it means opening one, hitting that unsubscribe link and following through with that on the web (they’ll try to trick you six ways to Sunday to stay subscribed), and then deleting the email. Don’t worry about them not honoring your unsubscribe or making you a target for more email you don’t want. There are literal laws against that and unsubscribing is effective.
Sometimes it does take a while though.