yes you can just manually enter summary gain loss by section (short term, long term etc). The issue is any adjustments e.g. wash sales, will trigger the need for the details and ask you to mail things in. The way to resolve that is to just enter the specific lots/sales that have the adjustment with all the details (dates, x shares of blah etc) which will generate form 8949 just for those line items, and then enter a summary entry for the bulk of the balance.
See also language on Form 8949 itself
"Note: You may aggregate all short-term transactions reported on Form(s) 1099-B showing basis was
reported to the IRS and for which no adjustments or codes are required. Enter the totals directly on
Schedule D, line 1a; you aren’t required to report these transactions on Form 8949 (see instructions)."
I have manually input all my 1099s for years, I have not found the import process to be worth the hassle if you have a lot of brokerages, and I prefer to organize it first to account for things like wash sales, or splitting up home state vs. outside state muni interest on 1099-INTs etc and there's always some sort of adjustment needed anyway unless situation is very simple. I also prefer not keying my passwords into a third party product regardless of how secure they claim it is.
