Are you sure you really need snappy? Snappy was important several years ago, but now gpt has many more operators, so has replaced many snappy uses. As you have seen, snappy can be tricky to get working. Teradue snapista makes it easy to create gpt graphs using python tools.
Your build of jpy looks good, but may not have used the same python as you used with snappy_conf. You should check again for multiple Python versions: ls -l /usr/bin/python*, which -a python, and which -a python3. Various linux packages depend on different python versions, and there are often system tools that require an older version of python,
so I never encounter systems with only one version of python. After upgrading Ubuntu to 21.04 I have two versions of python:
gwhite(hippo)@gwlaptop /mnt/c/Users/gwhite
% ls /usr/bin/python*
/usr/bin/python3 /usr/bin/python3-config /usr/bin/python3.10 /usr/bin/python3.10-config /usr/bin/python3.9 /usr/bin/python3.9-config
% ls -l /usr/bin/python
ls: cannot access '/usr/bin/python': No such file or directory
On older versions of Ubuntu, ‘/usr/bin/python’ could be python2.7, and python3 should be the oldest python 3.x version and is used by “system” scripts.
Having jpy installed in Python shouldn’t hurt, but snappy_conf looks for the binary wheel and installs jpy in the $HOME/.snap/snap-python/snappy directory. You have not been consistent in your use of python:
I don’t think this is a problem, since snappy will use the jpy install in the snappy directory. Using pip3 is one of those bad practices being propagated on internet sites. You should use /usr/bin/python3.x -m pip to ensure that the installation goes to the desired python version.