You could do this with a report based on the "Last tried" field. Last tried will be updated when an asset was attempted to be scanned but the scan attempt was not successful. If a scan is unsuccessful this would indicate the asset is offline. You can put this report on one of the dashboards afterwards.
Do note that in order for this to work, you will have to scan your assets quite often. To reduce the impact this might have on performance, I would recommend double checking your scanned item intervals which dictate how often specific Windows items are rescanned. Lowering the amount of items scanned with every scan will reduce scan times. More information about the scan item interval can be found here: https://www.lansweeper.com/kb/115/managing-how-often-specific-data-is-scanned.html
The scan to check if an asset is online or not can be either an scheduled agentless scan LsPush scan which is schedules to run multiple times in a day as Samuel suggested.
