The README says
In order to build each image, just cd into the directory and execute make:
% cd dev && make
Since there is a dev directory in this repository, one might be tempted to run that cd dev while in the checkout directory of this repo, to get to that dev. But there is no Makefile there, it is in the top-level directory of the repo instead.
Clearly the instructions want the user to cd into the checkout directory but given the name of the repo is build-edgetx, it is unlikely the directory name is dev.
Would you prefer a PR to remove the cd dev completely, or something like a sequence
git clone https://github.com/EdgeTX/build-edgetx
cd build-edgetx
make
?