v1.20.0
is Micropython (upstream) tag. It does not include LVGL, therefore lib/lv_bindings
git submodule is missing there.
If you want to build Micropython+LVGL you need to either use the master
branch or release/v8
branch, as described here: Micropython v1.20.0
I also suggest you try to clean/delete and build from scratch.