Regular, monthly payments from parents is an alien concept for me.
My parents and PIL have given us money for house deposits (around £30k total from my parents, over two house purchases and came from times when they had an investment mature and when they sold a holiday home, and £20k from FIL at first house purchase to help us get under a certain ratio for interest rates).
Other than that... I don't think we have had money from them. Apart from birthdays And Christmas from my parents. £70 each. They are generous with our DC at birthday and christmas and look after them during school holidays for 3wks of the year. Oh, and my parents take me out for one lunch a year.
FIL has helped out SIL significantly over the years, lump sums and during a short period of significant financial hardship.
Otherwise, my parents and PIL are of the opinion that they worked hard for their money and retirement and will spend as much as they want doing what they want. Which is fine and their choice.
It would never occur to me that they could give me or DH an allowance. Or regular money. Or just give us cash for a holiday or buy us a car or nice food or anything at all. We are grown ups who have decent salaries and can pay for ourselves (or save up) and big purchases.
I do have some friends whose parents have paid of credit cards, or bought cars for them. When we were in our early 20s as well as more recently in our 40s and 50s.
To me, it feels a bit like playing at grown ups but still having your parents being the actual grown ups.
I am chronically self sufficient though. My parents have always been more supportive of my sibling (emotionally as well as helping them out with big financial purchases and holiday costs) because of medical needs. I don't begrudge my siblings, but it may feed into my thoughts that as I don't have a specific need for help, then I dont expect it.