My server keep saying "Can't keep up! Is the server overloaded? Running 2185ms or 43 ticks behind"

Thank you for your report!
However, this issue has been temporarily closed as Awaiting Response - this does not mean the report is not valid, we just need more information to verify it.

While the lag occurs, please run /debug start, wait a while and then run /debug stop in order to create a debug profile. Afterwards, run /debug report.

If you do not have the permission to run these commands, open your world to LAN and enable cheats. If you're on a server, make sure that you're a server operator in order to execute these commands.

Then, please attach the profile results found in [minecraft/debug/profile-results-<DATE>.txt|https://minecrafthopper.net/help/guides/finding-minecraft-data-folder], as well as the debug report found in [minecraft/debug/debug-report-<DATE>.zip|https://minecrafthopper.net/help/guides/finding-minecraft-data-folder] here.

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Is there a large amount of redstone running simultaneously on the server?

there is only one simple redstone running

What about CPU, does it use a lot of that?

the utilization is about 20% - 30% 

there is only debug result in the debug folder

nvm, I found it

my server is keep spamming "can't keep up " in the console like crazy

did I make the server incorrectly or what is wrong with it?

Please check if that's still an issue for you in the latest 1.16.4 stable release or the latest 1.17 development snapshot.