I add those destination email addresses to the system filter as a hard reject. I assume the other end will get the message eventually.
Even having a "it's not me" link doesn't always help if they use a different email each time - for a while, I was getting 3-5 Russian Instagram "confirm your email"s a week and the "it's not me" made no visible difference.
What bothers me a lot is that there's an active account attached to my email address with dozens of companies I did not choose to engage with. It as astonishing how few companies allow you to disavow an account created with your email (practically none. I don't have an instagram myself but my email account does.)
Marking their emails as spam just means I will no longer know what's being done "in my name" (with my email address). It doesn't aftually solve an issue in any real way.
The latter is risky though; some sites use email validation as proof they should attest to the real world identity of the person that owns the account. (Github is one such example).
I imagine some site does that and also does not ensure that access to the email address is enough to reset the password and 2FA setup. (Come to think of it, Github is also an example of this.)
Either way, common courtesy would dictate waiting a week or so between emailing and nuking the account.
What drives me insane is that 99 % of companies send "please confirm your email address"... And then have NO link to say "that's not me!". You can click for positive confirmation but you can click for negative confirmation. And they keep the account even though it's unverified email. Even though I never verified the email, I'm subscribed to ridiculous amount of Financial, retail and other services throughout Europe due to this issue (people inadvertently subscribing with my email address).