In Europe now that Russian gas is not on tap?

Building new nuclear plants would be a silly response to the current energy shock in Europe, since it would take so long for new NPPs to come on line. Renewables to reduce gas demand make much more sense, available both more quickly and more cheaply.

Why not do both?

I don't want to be here in 30 years time wishing we'd built reactors 30 years ago (which is where we are today)

Why not? Because it's economically pointless to build more nuclear at current prices.

The current situation where you might regret not having built more reactors 30 years ago is not comparable. Renewables were not competitive with nuclear 30 years ago. But that situation no longer obtains.

Renewables require backup generation. And usually that's gas burning powerplants because they have very short startup times. Main reason for wild prices of electricity in EU is gas supply crisis.

As response to the loss of Russian gas, renewables don't have to replace all fossil fuels. They just have to reduce fossil consumption enough to compensate for that loss.

Eventually, all fossil fuel use must be replaced, but that has nothing to do with the issue of responding to Putin that I was addressing. And the backup generation can eventually be non-fossil also, particularly hydrogen. Europe has massive amounts of potential capacity for underground storage for hydrogen, far more than would be needed.