I’d expect about 20% from what you described.
If your system is putting alongat one level and suddenly is not… Figure out what changed.
(what updates have you done recently)
What version are you running vane you looped for known Cpu load issues.
I appreciate you say ‘next to nothing’ but as an ex perf engineer. ‘I believe what the perf counters tell me’ (even a previous well behaved component may have issues like locking up a core, memory pressure not relieving handles etc etc.)
Cookbook has techniques for learning what’s going on I think the troubleshooting section has Cpu stuff.
You’ll need system monitor showing Cpu.
If it’s ‘homeassistant core’ showing hi Cpu it’s an integration. Disable half of them. If it stops it’s in the half you disabled if not re enable them and pick half of what was remaining. Continue until you isolate the bad component driving Cpu. If it’s not core the monitor should point at what’s driving the Cpu.
If you’re on less than 2025.9.3, 9.1 and 9.2 have a Bluetooth bug that drives Cpu up. That bug locks a Cpu core. Looks lime yih have three cores assigned. I take one away it’s approximately 33% of your Cpu +20+overhead? Yeah you’d hit 70% fast and it would feel like a boat anchor.