That's completely fake. The $750 was nothing to do with actual tax. It was an admin bill, like a registration fee. Trump submitted his tax returns ages ago. He did the same as I have done in the past. You get fined if you don't pay your tax on time, so while any tax queries are being sorted out, you pay an amount in advance that will more than cover however much you think they will work it out to, then you get a refund of any excess you paid after it's all sorted, or you can leave the balance in your account for next time.
He paid multi-millions in advance tax. That won't show in his account as tax paid until the final reckoning. They're still trying to figure out how much he actually has to pay because there is a lot of figuring out and always a bit of negotiation with massive and complex accounts like he has. The amount will be deducted from the money they are holding on his behalf, then he'll get a refund of any excess he paid.
They're being very economic with the truth. What they're saying is that there is no entry in his tax account as tax paid because they haven't yet worked out what it should be, but they know he's paid money on account.