Project can't find referenced projects

4>------- Started building project: m24-CommandBasedApplication
2>Microsoft.Common.CurrentVersion.targets(1844,5): Error MSB3202 : The project file "../../../../../../../mnt/user1/03_DATEN_1/Programming/C#/m24/m24-UsefulExtensionMethods/m24-UsefulExtensionMethods/m24-UsefulExtensionMethods.csproj" was not found.
2>------- Finished building project: GenshinMaster.Avalonia. Succeeded: False. Errors: 1. Warnings: 0
3>Microsoft.Common.CurrentVersion.targets(1844,5): Error MSB3202 : The project file "../../../../../../../mnt/user1/03_DATEN_1/Programming/C#/m24/m24-UsefulExtensionMethods/m24-UsefulExtensionMethods/m24-UsefulExtensionMethods.csproj" was not found.
3>------- Finished building project: GenshinMaster.DbModels. Succeeded: False. Errors: 1. Warnings: 0
4>Microsoft.Common.CurrentVersion.targets(1844,5): Error MSB3202 : The project file "../../../../../../../mnt/user1/03_DATEN_1/Programming/C#/m24/m24-UsefulExtensionMethods/m24-UsefulExtensionMethods/m24-UsefulExtensionMethods.csproj" was not found.
4>------- Finished building project: m24-CommandBasedApplication. Succeeded: False. Errors: 1. Warnings: 0
Build completed in 00:00:01.192