I do negligible miles, but an oil change before it goes into hibernation is about £50 and means bearings and parts all sit in clean oil ready for the spring.
Brake fluid isnt as important . I was discussing this with my neighbour last night. For a typical road car, then flush every 3 years , but the synthetic fluids now dont absorb water or hurt caliper seals like they used to. Ironically, we are going to his workshop next week to flush mine.
Coolant for my Skoda is 5 years , although he tested it and said it was fine, even though I have a 5 ltr of it in the boot. I suspect BMW is similar.
Watching RE Performance on youtube, looking at a messed up McClaren engine, as had track mileage on it and infrequent oil changes, recently, he has said the damage is caused by oil changes not being frequent enough. So, the owner has 8 grand of parts for cams, followers , phasers and other items. So, its not just the bottom end that old oil can hurt. I know we arent driving such supercars , but the principal is the same whatever the engine.
Sensibly a track car will have a more regular servicing regime, but road cars sit idling for long periods of time, not getting up to temp and still getting stresses , so a little love will make a big difference to how it runs and longevity of all internal engine parts.