Why is my 2018 tax return 121 pages long?

[DoninGA]

Because it not only contains your completed tax return forms and schedules, it also contains all the worksheets and informational pages for your tax returns, both federal and state.

[Critter-3]

Every year, after you file and before the end of the Online season the end of October, log in and  save a PDF of the return as filed.  Once the returns have been archived the only option you will have is the PDF with all the worksheets included.