Thanks for reaching out. We're sorry for the trouble with Lightroom. We're here to help.
Lightroom & Lightroom Classic Sync images & other details back & forth; however, presets are not synced.
When you launch Lightroom first time on a machine where you already have the presets in Lightroom Classic, your presets are carried to Adobe Lightroom & the cloud. (https://helpx.adobe.com/lightroom-classic/kb/sync-faq.html)
Adobe Lightroom does not store presets & other data in its storage, whereas Lightroom Classic & Camera save the presets in a shared location (C:\Users\<username>\AppData\Roaming\Adobe\CameraRaw\Settings) unless specified differently.
If you have the original preset files, you can import them into Lightroom Classic again.
Now, it will take some extra effort if you don't have the presets on your computer.
- You can right-click on each of the presets in Adobe Lightroom's presets panel & select Export Preset.
- You can apply all the presets to images & let them sync to Lightroom Classic & in Lightroom Classic, select the image & create new presets based on the applied settings.
Both of the methods might require patience & manual effort. We hope you understand.