I have a small problem that you do not find so many answers. But when you search for your domain on Google you get a hit where it says - The member you specified is either invalid or doesn't exist.
The owner had a member who was spamming and they deleted the account.
How to get rid of this?
There's not really a good way to get rid of these, I'd recommend updating your websites Sitemap and making sure the most up-to-date version is linked to your Google Webmaster account.
If I’m not mistaken MyBB should be sending the proper error response for which Google should respond in kind by removing the page over time.
Omar's comment is correct, however an updated sitemap may cause this to occur more quickly.
I personally always block profiles from being indexed, so yes, one option is to remove profiles from the sitemap for the removal to be faster.
(I'm assuming you use something like Google SEO that allows you to remove profiles from being indexed, but sitemap plugins that allow you to remove specific links can exists.)
You can also try by using to the Google Search Console, from where IIRC you can remove specific urls. The following might be outdated but you can search for more:
https://www.sistrix.com/ask-sistrix/goog...ch_Console
https://support.google.com/webmasters/an...9846?hl=en