He and the lege control it.
The state sets a value of wealth per child for each district. It can be anything they want it to be. School property tax on wealth above that value is "recaptured", i.e. sent to the state. School districts have some other options other than doing this, things like merging with another poorer district, but most choose to write a check. Lower the wealth per child or lower property tax rates and "recapture" goes down, meaning the amount sent to the state from the local property tax payer.
The state sets the amount of money a school receives per child. It can be anything they want it to be. If the school district does not raise enough money to cover that amount, the state covers the rest. In theory this comes from the "recapture" fund, but in reality the state just cuts them a check. Raise the amount of money a school receives per child and school funding goes up. Lower it and it goes down. Keep it it same during times of high inflation (and that is what we are doing now) and school funding goes down ... inflation eats it away.
Right now, these amounts are set such that the state is collecting more money than they are distributing, so the excess recapture money goes to the general fund. This general fund can be used for whatever the state wants.
The lege can pass legislation to change this but they need the governor also pass it, and he's not doing that. He wants private vouchers to funnel public tax money into private schools.
In 2016, some school districts sued the state saying that this was bullshit. They won. It was appealed to the Texas State Supreme Court. The court said no. The court said that things were screwed up, but everyone was at the wrong venue. The said everyone needed to work through this in the lege, don't take this to the courts.
And eight years later the lege and the governor are draining public education through inflation and inaction while building up the general fund for whatever.