As long as you have fulfilled the MOP of your HDB flat, you are able to buy a condo.
You are allowed to purchase a private/ resale condo and still hold on to your HDB provided your flat has MOP. If you have no outstanding loan, you are possible to loan up to 80% of the purchase/ valuation of the condo. If you have, up to 60% only.
If you need more clarifications, feel free to contact me.
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