Somewhere around Lightroom 7.3 or so, Adobe made significant changes to Develop Presets and how they are stored and organized. First off, the actual preset format itself has been changed from a .lrtemplate file into a .XMP file. This allows the presets to be used not only with Lightroom Classic, but also with Lightroom CC and Photoshop Camera Raw. This is a good thing as you can have one set of preferences that will work with all three applications. The first time you run Lightroom after updating from 7.2 or earlier, all of your existing presets will be converted to the new XMP format. (So far, so good.)
The other change has to do with where the presets are stored and how they are organized. No longer stored in the Develop Presets folder within Lightroom's larger Preset hierarchy, they are now stored in the Settings Folder within the Camera Raw support folder.
And this is where things get tricky. In the older days, you could place a folder full of presets in the Develop Preset folder and Lightroom would import them and retain the folder structure. Since the 7.3 update, this mechanism does not work as it once did and you have to jump through all sorts of hoops to get newly added presets to show up in their proper folders. (Now called Groups) If you don't they can end up loose in the User Presets folder or worse, not show up at all.
Fortunately, there is a free plug-in by John Ellis that can remedy all of these varies preset woes and get you back to the way things used to work. The plugin is called "Fix Presets" and will allow you to recreate the folder structure you have as groups within the Develop Preset panel. Or if you prefer, you can take all of the existing groups you have and recreate them as a folder structure on disk. Either way, you regain much better control over where your presets are stored and how they are organized.