I recently upgraded to 4.3, and ever since, my ScrollContainers are giving me this warning:

ScrollContainer is intended to work with a single child control.

Use a container as a child (VBox, HBox, etc.), or a Control and set the custom minimum size manually.

The thing is, all my ScrollContainers do only have a single child control, and their custom minimum sizes are all set manually like it says. Is there something else I might be doing wrong that's causing this warning, and if not is there a way to get it to go away? They also all seem to work as intended, so whatever the issue is, it doesn't seem to be affecting gameplay, at least not in any way I can detect, but I try to be careful with my structures to avoid issues down the line so if there's some subtle issue I'm missing it'd be good to know now.

Strange. Currently I play with ScrollContainers but with "4.3 stable" I don't get this warning.

What kind of child-node do you use?

Or do you use multiple scroll container as child of the TabContainer as mentioned by DaveTheCoder?

I get the warning for ScrollContainer's that have a single child of these types:
RichTextLabel
BoxContainer
ReorderableContainer (a custom class that extends Container)

I'm not using a TabContainer. That was the use-case in the tracker issue I linked. I'm guessing that doesn't matter.

If I weren't lazy, I would rebuild the engine with that one-line change (from the linked PR) added and see if it removes the warnings.

DaveTheCoder The fix should be included in 4.4-dev4 when it's published. I don't know if it will be back-ported to 4.3 as a 4.3.1 release (but my guess is "no").

The warnings are not present in 4.4-dev4. And I may be wrong about the fix being back-ported:

Many of the changes in this release are bug fixes that will be backported to Godot 4.3 and released in 4.3.1! So please test this release well so we can be confident with the changes and release 4.3.1 with them as soon as possible.

https://godotengine.org/article/dev-snapshot-godot-4-4-dev-4/