After a fair amount of trial and error I now have the Pebble SDK working on my Mac (macOS 10.15.4 Catalina). I was working from the guide here. I can now create, build and deploy programs and watch faces to my Pebble watch.

Firstly I had problems with the virtualenv command:

cd ~/pebble-dev/pebble-sdk-4.3-mac
virtualenv --no-site-packages .env
source .env/bin/activate
CFLAGS="" pip install -r requirements.txt
deactivate

It turns out the –no-site-packages flag is not required and should be omitted (see here for details).

I then had issues with no SDK being installed (and the scripts trying in vain to locate the SDK on the Internet). After trying:

pebble new-project testing

I was greeted with:

No SDK installed; installing the latest one...

Consulting Google yielded:

Cannot install SDK from pebbledevelopers

The key part of the reddit post is path to the SDK. I used the following to successfully install the SDK:

pebble sdk install https://github.com/aveao/PebbleArchive/raw/master/SDKCores/sdk-core-4.3.tar.bz2

The last fix was disabling the analytics tracking by creating a NO_TRACKING file in the SDK directory.

SDK Install Guide from pebble