Some files and folders have disappeared from my PC desktop

I turned on sync function of dropbox, and restart my windows, icons on my desktop were gone!

I use free plan so the icon in taskbar says it's full and I have to upgrade.

I realized that I was in the same situation with this person

https://www.dropboxforum.com/t5/%E8%B3%AA%E5%95%8F%E3%81%99%E3%82%8B/PC%E3%81%AE%E3%83%87%E3%82%B9%E3%82%AF%E3%83%88%E3%83%83%E3%83%97%E3%81%8B%E3%82%89%E3%83%95%E3%82%A1%E3%82%A4%E3%83%AB%E3%82%84%E3%83%95%E3%82%A9%E3%83%AB%E3%83%80%E3%81%8C%E6%B6%88%E3%81%88%E3%81%BE%E3%81%97%E3%81%9F/m-p/503116

so I checked Dropbox>PC>Desktop. There were folders I used to see. But there were only two folders in the folder(Folder-Self-Development) that I used to have more than ten folders. To make matter worse, In my "Portfolio", many files are gone! But in other folders, I can see exactly same files and folders ( The-Web-Developer-Bootcamp-2022 )

I am sincerely looking for someone who teaches me how to find lost ones.