Are you by chance using external storage media such as USB or SD cards?

The bus on these older model chromebook devices had a choking issue where the kernel would fully saturate the transfer bus and cause a cgroup scheduling strategy to give full priority to the processes using the bus at the expense of the gui. Solutions to this problem include a new NVME or software level cgroup reconfiguration of the kernel to revert scheduling priority to equal across all cgroups.

Or it could be something else entirely, but last time i had this issue and bug hunted it the finding was as stated above.