Two split ACs, dirty sock syndrome on both, UV is the answer?

Hey, I'm from the EU (R32 coolant) and I have a 3.5kW Midea Ultimate Comfort and a very pricey 5kW Daikin Ururu Sarara AC in different rooms far away and I've been battling both of them for years because they both smell like what I can only describe as 'geriatric mold' when cooling even after a full cleaning including disassembly (not just spraying inside).

The smell comes and goes almost instantly (lasting like ~30 minutes), but what I've recently noticed is the smell does not randomly comes, but 100% once they bought the temp down to target and just start idling and running the fans. But then it always happens! Hence, I've set my Daikin to 21°C and literally only turn it on when it's hot inside and turn it off at around 25-26°C before it can fuck off and start oozing that horrid moldy smell. This works really well in terms of smell but as you can imagine it's very annoying to manage.

It's not the drain pipe, we've tried that, there's no stagnant water in them, no pets, no sweat or old people lol, no mold anywhere in the house, not caused by cooking, no air refresheners with oil, etc, etc. Just a clean and regularily cleaned, basically spotless environment with regular ventilation and cleaning both ACs every 3-6 months! At least 6 different HVAC crews tried to solve it over the years but nobody could even though some told me they had run into this issue.

In the past I've used a DIY solution and put an UV LED strip on the Daikin and it seemed to work well, but that interior device is huge and UV eats away at plastic so that was just a short experiment so it wasn't really conclusive but I think it worked. Even if I disassemble the Midea which is smaller/easier to do so and clean it even with like a very strong ~15% hydrogen-peroxide solution (crazy but that worked the best all things considered) or any other AC cleaning solution the smell comes back within days!

But I can see there are now split ACs with built-in UV lights so I'm wondering if that's just some gimmick or do they really disinfect the inside (both the condensing coil and the cylinder fan)? The Daikin has all the bells and whistles and more filters and features that I could even list (no UV though), but it's still useless in terms of this dirty sock syndrome.

Sorry for the wall of text (I could rant about this forever), I thought more details should be better so here I am.