Hi there, Hijasmuhammed.
For now, we don't have an option to make 20 line items into a single line when copying an estimate into an invoice. I'll be sure to submit feedback to our Product Development Team when considering features to introduce in software updates.
QuickBooks aims to find new ways to make sure that your product meets your needs. I'd suggest visiting the QuickBooks Blog website to stay up-to-date on any improvements in the software.
Please keep me posted if there's anything else you'd like to add. I'll be around to help.