Since they are just headers, you could swap to using the Title parameter type instead of using the parameter group(?) function. That is if you want to remove the collapsible function all together.
It doesn't matter what the parameter type is - title, length, boolean, etc.
It is the dependency switch that controls the expanding arrow.
A dependent parameter will automatically make the parent parameter BOLD as if it was a title type, but it can still be any type.
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