The thing is the State of Florida unquestionably has the right to set curriculum standards for public schools. Saying what should and should not be instructed in the classroom isn't really a matter of constitutional law. However, and this is a huge 'however,' the way the law was actually being enforced was not limited to classroom instruction.
Opponents of the law like me have always said that the law was worded so vaguely that overreach must have been the intent. So, you're right that free speech rights did get implicated, and that's undoubtedly what motivated the State of Florida to settle the lawsuit. They know federal judges, even quite conservative ones, take a dim view of some of the expressive-conduct restrictions that Florida school districts were enforcing in response to the law.
The state's defense in the court of public opinion has always been that the law does no more than set classroom-instruction standards, so the lawyers for the plaintiffs said, in effect, "Fine, then put your money where your mouth is. Set state educational policy to align with that and tell the school districts."
The State agreed, presumably fearing the law in its entirety would be overturned.
That's the legal analysis. There are political considerations too, with the Florida GOP wary of signs that show DeSantis's culture war is turning many voters off.