When you create a new (user) preset, or update a preset that you created before, Lightroom saves that into a central folder.
This can be accessed by any Catalog that you may use, now or in the future on this computer. The only exception is, if you set the Catalog option "store presets with Catalog", then user-made presets are created and updated in a different folder, that sits alongside that particular Catalog's previews etc.
You cannot alter the Adobe supplied presets or change where they are stored.
There are several different kinds of named presets you can make: for importing, for renaming, for exporting, for watermarks, for printing, etc - not just the Develop presets that contain specific picture adjustments. All these have their own different storage folders and it is a good idea to know where these are so they can be backed up / copied to another computer. Note that if you copy presets into a computer while Lightroom Classic is runnning, it will not yet see these, until the program has been closed and restarted.
To find where presets are stored, go to Lightroom Settings, Presets tab, Location section - there is one button for finding the Develop presets specifically, and another "show all other" button for finding a folder called "Lightroom" which contains other stuff specific to LrC. Alongside that is another folder called CameraRaw. This contains all user-saved files that Lightroom Classic and Adobe Camera Raw share (including the Develop presets), so both those folders, Lightroom and CameraRaw, should be backed up elsewhere, to protect the work you have put into those, from being lost if you have a computer problem.
Besides this, your imported files (whatever disk storage they live on) should be backed up and also the Catalog should be backed up - somewhere other than your current computer storage - to protect all that also, from any loss.