The platform itself is quite lean regarding resource consumption, so things like bottlenecks are usually related to the workloads. I recommend you start with the Troubleshooting tips in the documentation:
https://docs.harvesterhci.io/v1.1/troubleshooting/installation
You may see that a tool called supportconfig is mentioned there several times. If you are a paid customer, that's what you should use to send info to our support colleagues,. If you aren't, it's also useful as it's a package with all the relevant logs altogether. Use it and try to look for errors/warnings in the collected logs. If there's any type of hardware failure or misconfiguration, it's quite likely that you'll something there. If it's a bottleneck or something related to performance, it may not be that obvious, but think about what your VMs are doing and try to follow from there. I hope it helps.