Can you confirm that your watermark is in your catalog settings folder in the Lightroom folder? Open Lightroom folder in your pictures folder and look for the Lightroom Settings > Watermark folder.
If your preset is not there > go to the Settings > Presets tab in Lightroom Classic and find it by tapping the Show All Other Lightroom Presets button. Once you locate it move (or copy) your presets to the appropriate settings folder. If you check the Store presets with this catalog you will prevent that from happening with future updates.