Is it possible to bootstrap an enterprise SaaS company?
Yes. It just takes longer to get to Initial Scale.
Qualtrics was bootstrapped to $100m ARR+. More on the story with the CEO here:
Atlassian was bootstrapped, essentially, to $300m ARR. The venture round was for secondary liquidity. More on that story here with Jay Simons:
There are many others.
But most of them grew a lot, lot more slowly to the first $10m ARR, and almost all start at the bottom, with smaller customers, self-service, smaller deal sizes, etc.