Make a filter that takes any email with the word “unsubscribe” in it and punts it directly into archived mail, rather than sending it to your inbox. Since nearly all marketing email has a footer that explains (in very small type) how to unsubscribe to the mail, all of it will now bypass your inbox and you’ll mostly only see the mail you actually want to see, from actual humans you care about. You can still see the marketing email (and anything else that might have been sent to the archive) by clicking on the “All Mail” tab, so you won’t miss anything; you’re just prioritizing what you see.
“Why not just unsubscribe to marketing email when you first get it?” Well, see. I often do, but a) sometimes I do actually want the marketing mail, I just don’t want it cluttering up my inbox, b) this is easier than unsubscribing to each thing.
(Mind you, what I really want it what Inbox, the alternate mail client from Google, used to do, which is to figure out what emails were marketing and put them all into their own daily single-line category in my inbox, where I could look at them, or not, or archive them or not, at a glance. But Google decided to can Inbox and hasn’t ported that functionality into GMail, so this is the next best thing.)
This is a really simple filtering trick which honestly I should have thought of at least a decade ago, and now that I have, it’s almost shocking how much it’s improved my email experience in general. If you’re using GMail I genuinely suggest you try it. I suspect you’ll be glad you did.