How to find source formula of brew package (github repo)?
If your package is in homebrew-core, then you can view the recipe's ruby source and its changes from the homebrew-core repo in the Formula directory

https://github.com/Homebrew/homebrew-core/tree/master/Formula

Unfortunately, finding the recipe for a given brew package on github.com may be tricky, since there's too many dirs and GitHub may truncate or refuse the output.
Instead, you can get and list all the homebrew forumulas with the following commands in zsh:
git clone https://github.com/Homebrew/homebrew-core.git
cd homebrew-core/Formula
find . | grep -i &lt;package&gt;

Then you can show the history of a given formula with git log
For example, I was able to discover that the python@3.7 package in brew changed yesterday:
user@host ~ % git clone https://github.com/Homebrew/homebrew-core.git
Cloning into 'homebrew-core'...
remote: Enumerating objects: 77, done.
remote: Counting objects: 100% (77/77), done.
remote: Compressing objects: 100% (34/34), done.
remote: Total 791472 (delta 51), reused 59 (delta 43), pack-reused 791395
Receiving objects: 100% (791472/791472), 316.25 MiB | 9.55 MiB/s, done.
Resolving deltas: 100% (529456/529456), done.
Updating files: 100% (5476/5476), done.
user@host ~ % cd homebrew-core/Formula
user@host Formula %

user@host Formula % find . | grep -i python
./python-yq.rb
./boost-python.rb
./python-markdown.rb
./app-engine-python.rb   
./ipython.rb
./python@3.7.rb
./gst-python.rb
./micropython.rb
./wxpython.rb
./reorder-python-imports.rb
./python@3.8.rb
./boost-python3.rb
user@host ~ %

user@host Formula % git log master -n1 python@3.7.rb
commit 10d3df6c9a263c4e7dea4752a00a1b98ddc9c05a
Author: BrewTestBot &lt;1589480+BrewTestBot@users.noreply.github.com&gt;
Date:   Wed Sep 9 00:40:17 2020 +0000

    python@3.7: update 3.7.9 bottle.
user@host Formula %