I have a generic name gmail account and people with my name frequently accidentally use my email address when signing up for stuff.
When I get unsolicited mail which doesn't include a simple unsubscribe link then I just report as spam instead.
Also, a lot of companies nowadays keep adding weird email topics that you need to constantly unsubscribe from.
If I signed up and turned off all subscriptions, then anything they send is marked as spam immediately. The lack of cost in sending email makes it easy for them to keep abusing all the time.
Mark it as such.
And, as others have noted, unsubscribe cannot involving going and logging into their system. If I need to do that, it generally goes directly to spam.
My gut says unsolicited marketing emails, from popular sites I've never used before, like Brooks Brothers or Robinhood (especially after a "Welcome to ${site}!") or US public school event notification emails are all probably legit mistakes.
I could see even a public school system having issues with getting flagged as spam if they don't include an easy method to unsubscribe because then marking as spam+blocking becomes the best option in response to wrong address.
Which of course you click and then have to go through a number of hoops to log in, confirm Email address, authenticate, etc.
At this point, I just mark those as spam as well.
I've noticed a recent trend where unsubscribing actually does nothing
Catchy subject seemingly target to me. Same for content.
But you are right, it's more likely enough users marked them as spam that Google algorithm decided the source is the spam.
https://support.google.com/mail/answer/15263077
Constantly receiving email from one alias is fine since it signals a subscription-like communications. Recycling through different aliases for the same recepient is surefire way to get flagged.
If you want to "personalize" the email, just add the name of the marketer in the subject or footer.
Hey fontawesome and any other company that sends bullshit spam, nobody cares about whatever thing you want to spam, you're just poisoning the well for others.