Looking solely at electronic direct payments, it would be more than a billion transactions per day, there are multiple major schemes that work on the 100m/day scale each (Visa, Mastercard, US ACH, EU SEPA, China Unionpay, etc) and a lot of smaller ones that add up. So that's in the ballpark of 10k sustained average txn/sec, more in peaks.
On the other hand, there's room for a lot of growth, it's not even a single transaction per day for the almost 8 billion people that we have.
Which is the core point: the major processors aren't being limited by their technology, they're being limited by the size of the economy. There's no real meaningful limit on how they can scale that.
Just barely creeping across the line with crypto means its already inadequate.
On the other hand, there's room for a lot of growth, it's not even a single transaction per day for the almost 8 billion people that we have.