Hello @nadeamer
In this case you are exceeding the following quota from Quicksight that you can check from the Service Quotas console:
L-AECE65ED - Calculated field expression length
The max limit for this quota is 250,000 characters and unfortunately you cannot increase it further.
You should be able to create new calculated fields by shortening the expression used on them to contain 250K or less, also remember that you can reference calculated fields from calculated fields so this could also help you on reducing the length of them.
Hope it helps!