Silly question, but I mean, no tech history I've ever read bothers to go into the invention(s) of doors!
Hi, since this question reaches way back into prehistory, it may be worth x-posting to our sister sub /r/AskAnthropology, or /r/Archaeology. While there are some archaeologists here - and you might get an answer here - there are more in those subs, and with greater focus on earlier time periods.