However, have worked it out

https://neosmart.net/wiki/fix-realtek-audio-delay-lag/

Did that, rebooted, now I get all the audio buffer size options, can set to 128 samples.

So it was the realtek audio driver at fault.

Agree with jcitron, an external audio device is certainly worth considering. Not just for lower latency (in it's portion of the whole audio latency loop) - but also, it may include benefits like better 'headroom', better DAC and various other things, giving better overall sound too. To make it more useful, it also will handle a lot of processing which will give your PCs CPU some extra room to process things (background processes etc.) better with fewer glitches/limitations, while getting on with piano/recording/playback.

BTW I had a previous laptop (similar vintage) which had a slightly faster internal audio latency loop than my current higher spec PC tower. I built the new one for speed/power etc.. but it's like yours, slower internally then my old lappy.

The benefit though, of a good external audio unit (connected over a fast USB 3 in my case) is that, it can run smaller buffer sizes etc.. and ends up shortening the entire latency loop - faster overall than the old machine could get. But for piano playing, I like some latency depending on the piece.. so getting quite a lot closer to zero latency (in Pianoteq's numbers) for piano is to me not a reason to get lower and lower latency.. but it's possible if it is your goal.

Adding these for OP and/or any readers passing thru, as they are useful for doing other things to get a workstation humming along better:

First thing maybe to check:

ASIO4all - Universal Windows ASIO Driver

(or ASIO drivers at all.. just to be sure you're not struggling without at least ASIO first.) Or maybe your sound card supplies an ASIO driver bundle to install. I'm almost certain Fancellu does/did.. but putting this here for any readers because, I've found many have overlooked this bit, and find their soundcard stuttering etc.

Some other very basic things to look for include, removing unnecessary apps (or stopping them from 'startup'), esp. apps which use audio in some way.. and certainly turn off or remove 'helper' apps which may do things like 3D audio, or some spatializing (different names like 'theatrical mode' audio.. some are like bloatware which often comes installed by default but much of it can be removed and it can help you get on top of your own audio).

This is my recommended guide for checking though "What have I missed?" to get audio working as well as can be expected on our machines (it's a free and I believe very helpful resource which has been around a while and seems updated over time)..

Glitch Free is a guide for getting better audio results - by Brad from Cantabile - Software for Performing Musicians

Hoping some of that helps OP or others getting better performance - but certainly, I'd recommend an external audio unit for many reasons beyond latency.

New pc is win11, amd 7950x

i.e. audio buffer is 480 samples (10ms) @48k hz

On my old pc (i7-3820 from 2013!) it offers from 128-448 samples (2.7ms to 9.3ms)

Any idea why?

Is this built in audio?

This can be really poor depending upon the hardware. You may want to invest in a discrete sound card as that will give you more options and better sound.

i.e. audio buffer is 480 samples (10ms) @48k hz

On my old pc (i7-3820 from 2013!) it offers from 128-448 samples (2.7ms to 9.3ms)

Any idea why?