In 2010, you came across a site that was giving away bitcoins. The site said it was free money so you signed up. You were logging in to figure out how it was money but couldn't. The last time you logged in you had more than 100 bitcoins. Later you forgot about the site until 2017 when a ponzi was advertising Bitcoin. Bitcoin? The name rang a bell and you stated hearing stories. You remembered you must have many bitcoins somewhere but you can't even remember the name of the site. How would you recover your BTC?
First thing, we must have a record in all sites that we've been registered but I'm doubted if you have these things cause you can't even recognize which site it is. From this certain scenario, I don't see a way to recover it cause you have nothing to look by and even just a hint still don't have. Ut is better to forget that 100BTC and move to another story of your crypto life. And consider this mistake as a sort of learning and knows the importance of having back-up records of all important files.