Very Slow running mac

Hi there, can anyone help?

My mac computer is running so slowly that it's becoming impossible to work on it. I have OS 10.15.17 installed, I have 797 GB of 1TB available memory. I do have a message when I use photoshop saying I have insufficient VRAM to run my graphics processor and that it is incompatible, which is a fairly new message, but would this slow everything else down including writing and saving documents and emails or even opening files. Any ideas of how I can fix this would be amazing as it's so frustrating trying to get anything done. Also, weirdly, it gets much worse later in the day. I am in England.