Windows has tons of dynamic tasks it runs at different times. For example, there's over 100 scheduled tasks that trigger at different dates, times, and on different events. And then there's even scheduled events that occur from the registry too. In W10 (not sure yet how W11 handles this one), but SMB file sharing is installed by default. It's not used by most home users though and so it detects how many reboots the system has had without utilizing this service. If 3 reboots pass without it being used then Windows uninstalls it. I could be missing some detail, like maybe it has a secondary check too, but it doesn't really matter, the point I'm making is there's a lot of background activity in modern Windows that kicks off all the time, even while the computer is undergoing heavy usage.
Ontop of that, there's even bugs at play too that haven't been entirely fixed over the years. Indexer and sysmain for example have both been thoroughly documented to eat up 100% cpu while you are doing a heavy task, such as playing a game, and have either a memory leak or a bug in the code that causes literally all ram to be consumed until the computer crashes. I don't think the problem here is LatencyMon, but rather just the complex beast that Windows has become. So much of this activity happens without the user knowing which can lead to all these mysteries.
There's some other concerns here too, your LatencyMon shows that WMI sees your processor as only being 30 Mhz, while the registry sees it as 2995. If you go into your bios and start disabling the features causing this, such as Speed Step, and all the other related settings such as Hyperthreading and so forth, you'll very likely see noticeable DPC improvements, as well as the Mhz rating changing in LatencyMon. I'm not saying this is like an across the board fix for everyone, but is stuff that should be investigated at least. DPC issues start in the BIOS first, then it's drivers responsible secondarily, then Windows third.