Will my custom presets be lost if I use the uninstaller? How can I save them?

If you install Nik Collection 4 by DxO over a previous version of Nik Collection by DxO, presets will be migrated automatically to Nik Collection 4 by DxO. If you choose to use the Nik Collection 4 by DxO uninstaller to uninstall a previous Nik Collection by DxO version, be sure to check the checkbox to keep custom and imported presets, or they will unfortunately be lost.

Please also see this article: https://support.dxo.com/hc/en-us/articles/115015301507