My opinion is that we should not get too enamoured with most rules of thumb - don’t fall in love with specific shares and don’t blindly accept adages like “don’t time the market” without thinking what that really means.
Your thoughts here on cash conversion are not necessarily a bad plan (also see What is going on today? - Megathread - #2410 by bitflip). As you approach retirement age you should change the proportions by which you allocate assets. So for example increasing the cash and bond aspect. If you have a company pension with some sort of “Lifestyle choice” then you will see that is exactly what is done, by your pension manager, for security purposes: over many years the proportions gradually and smoothly change. The rationale being that you don’t want a dramatic drop in pension value at retirement date because of Market turbulence.
You can cut your losses in a sustained drop in the market by pulling out. The risk you take is that you lose some of the gains on the way up. That is the call you make. And your retirement date should feed into that risk strategy. Also it matters whether we are talking ISA or pension here. Especially because you have to make a decision on how you want to take the pension (annuity, gradual sell off and so on and so forth).