excel suddenly became very slow and clunky today

this lag happens only when i open an existing file in my local system.
when i open a new workbook, it works fine and without that sluggish lag, however the moment i save it onto my pc, and re-open, there is a lag sort of like a slow motion effect that is really bugging and slowing down my work performance.

settings i have turned off:
co -pilot
auto save off
turned off 'enable background error checking'

i am not sure whats going on, this is not a big workbook/many formula kind of issue as even a brand new blank file which i save, it becomes lag afterwards