Is there any possibility to have the option to restrict the player from entering dimension(s) X until unlocking advancement(s) Y?

It would be nice to choose if a player needs an item and/or an advancement in order to enter a given dimension. Thank you.

That is how it works, but the mod dynamically generates advancements based on the config although you can override the unlock advancements with a data pack and that will unlock the dimensions.

Example Data Pack attached.
zCustom-RP-Datapack.zip

Added to the Wiki - Custom Advancement Datapacks