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At which point of buying real estate in Dubai you can get Dubai bank account?

You don't need to own a property to have a residence and bank account there. Residence by owning property is available only as golden visa - so very expensive and doen't make much sense
https://u.ae/en/information-and-services/visa-and-emirates-id/golden-visaReal estate investors
If you own a property or a group of properties, you may be granted a Golden visa for a period of 5 years, renewable on the same conditions and without a sponsor subject to the:
  1. provision of a letter from the land department of the respective emirate stating that he owns one or more properties whose value is not less than 2 million dirhams
  2. purchase of a property with a loan from specific local banks approved by the competent local entity.