What do you do when every client is different?

It takes time.

Understanding requirements. Evaluating tools. Estimating (which is always wrong anyway). Writing a proposal. Chasing for an answer. Then scope creep and change requests.

It all takes so much time.

But why is that?

It's because you've made it that way.

You say "I build websites", when you could say "I build booking systems for dentists".

Imagine how quickly you could get it done if all you built were booking systems for dentists? You'd get really good really quickly.

What will you do with all that free time?

And you could charge more - because you're the go-to expert for dentists who need a booking system.

But, you say, “I'll never get enough work”.

Let's say you can build a booking system for a dentist in one week.

That means, to be really busy, you need around 50 dentists per year.

There are 41,000 dentists in the UK.

Can you really not find 50 who need a booking system?  When you’re to the go-to expert in that field?

And then think of the extra time you have because you're not starting from scratch.

You can use that time to learn something new.

Or start a side-business.  Maybe "booking systems for physiotherapists"?