This is a quite incredible thread, OP.
You sound very resentful and angry about things most people don't get from their parents and not at all grateful for the things they did give you (supporting you at home when things went wrong, money if I understand that correctly).
They are living a long life and in that long life, properties and money change hands. I also had property I sold that in hindsight might have been better to keep, but at the time, the mortgage or the service charge or even just the hassle was too much. I suspect the same was similar for your parents. Ultimately the properties were left to them and they used them to support your lifestyle as a child and their lifestyle as long-lived adults. This is pretty normal stuff.
Properties in other countries also devalue when unattended, buildings crumble, you have to pay not only service, but water, tax, electricity if you want to use it, and if in a shared flat there will be lump sums that have to be paid if something need redecorating or redoing which is every few years.
In short, you seem to blame even living in a boring place on them! And your boring job through lack of their direction?
You do sound down and I think seeing the GP about depression and getting some therapy would help you start to reframe some of this stuff.
It's fine to have a feeling of 'oh, I wish they hadn't sold that central London property', my children probably have it too, but that's the ups and downs of life. It's not fine to blame your entire life on their lack of foresight and knowledge of the economy and housing market for the past 30 years.