Please post your System Information as Lightroom Classic (LrC) reports it. In LrC click on Help, then System Info, then Copy. Paste that information into a reply. Please present all information from first line down to and including Plug-in Info. Info after Plug-in info can be cut as that is just so much dead space to us non-Techs.
Could it be possible that lightroom lost my photos?
Please provide the information requested by @GoldingD. Also please note that no version of Lightroom "loses" your photos; almost always when this happens the photos were moved or deleted by the user or other software or hardware malfunctions.
I use lightroom and Appel tells me that the problem comes from the lightroom cloud.
Please explain this in a lot more detail, explain step-by-step what you did, and show us a screen capture of the problem. Please tell us the exact word-for-word unedited error message.