I don't see how I could figure that out. Credit reports don't show cards which were cancelled 10+ years ago, so all those credit cards that I got while pursuing lifetime AA elite status (while miles from all sources counted toward that until 2011), etc, I have no way to count them.
Right now Experian shows almost 20 open accounts and just over 40 closed accounts for me, but I recall it showing close to 60 closed accounts a few years ago soon after I signed up for (the free version of) Experian online.
I still have a Discover card account that I opened in the late 1980s, and a Citi card account that I first opened in the early 1990s (though I've product converted that card a couple times, it kept the account history through those product conversions).
But I know I had at least one credit card before that Discover card, but it was a credit card that was discontinued decades ago.
So I'm guessing I must have had well over 100 credit card accounts since I started getting (then often cancelling) more cards for signup bonuses starting in the early 2000s, but I don't know how to figure out just how many.
Note: Back in 2000s, there didn't tend to be anti-churning restrictions of the kind that several banks these days, and meanwhile each card gave a much smaller signup bonus (AA cards only gave 25k bonus miles each for something trivial like $250 or $750 spend), and so you had to get a lot more cards to get some meaningful amounts, compared to today.