Illustrator crashing and 'can't copy the objects' error

I have spent hours trying to resolve an issue where Illustrator continually crashes when I am trying o work on a document. It either just crashes or I get a 'Can't copy the object. There isn't enough memory. ID: - 108' error. The image then turns black and white and the programme crashes. I have bought an external hard drive and have saved documents to the Cloud but this is still happening. Is there a way to fix this? I'm using version 26.5. Many thanks.