There is a bug ion Lightroom classic where you cannot remove a preset. Regular Presets remove fine on the export panel, but if it has any Postprocess action (I use Jpeg Mini and Metadata Wrangler ) you cannot remove the preset. Even if you remove the post process action, you cannot remove the preset. When you select it the remove stays greyed out and the action activates automatically (even if you removed it a few seconds ago from that preset).
The only option you have is to select the preset (remove is greyed out) right click and delete.
I think this is a bug and confusing users. The remove option should be not greyed out and work properly when you want to remove a preset even if an action is bound to it.