E-mail from National Conference of State Legislatures to Seth Barrett Tillman:
That number is always the last to pin down [and not yet final] and the one with the most ‘noise.’ Our current estimate is that Republicans netted at least 160 seats in the  election. It is rare, but far from unprecedented, for the party winning the White House to lose seats in states. This is the 6th time that it has happened since 1960, and the most losses by the winning president’s party since then. In 1960, Democrats lost around 300 legislative seats even though John Kennedy won the White House.
The reader can reflect on that comparison—to the election of 1960.
Seth Barrett Tillman, How did the Parties do in Relation to State Legislative Seats?, New Reform Club (Nov. 18, 2020, 9:34 PM), <https://reformclub.blogspot.com/2020/11/how-did-parties-do-in-relation-to-state.html>;