Never heard of BlueJ. It is apparently a Java app. Such things are extremely fragile. You should assume that it won't work. Depending on what Mac you buy (Intel vs. Apple Silicon) you may be able to hack on it and get it working. No guarantees though.

You can't put code in a Resources folder. 3rd party umbrella frameworks are also not supported. The .net framework will need to be a sibling framework. Since you are doing this manually, you may also need to manually adjust the paths of your framework using "installnametool" so that it can find the sibling framework.

Submitted a bug report and DTS ticket. I have a demo app that easily demonstrates the issue. At 1.0 quality, all other formats, including JPEG, are apparently lossless. HEIC is obviously lossy.