You need to hold the starting settlement landmark for a turn as Eshin to start the research tree.

A workaround with this mod is to use
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1574469690
and paste this in the text box on turn 2:

PJ_SS.dow_main_ui_button:SetVisible(true)

then press Enter, and Execute, you'll see the button appear again, and you can use it

OR

use my Console Commands mod and type "show css" on turn 2 instead

OR

just use the Mod Configuration Tool option that keeps the buttons always visible.