I heard that you are not allowed to get angry in Ramadan. Sometimes when I’m working on something I may get frustrated as it can be difficult and such. Would this be permissible?
Yes that's permissible. Anger is a natural emotion so it cannot be avoided
What is meant by 'do not be angry' is to not loose control of your anger and start shouting, being aggressive etc. If it's just an angry feeling not unleashed, that's ok