So, I have followed https://www.electronjs.org/docs/tutorial/using-pepper-flash-plugin and have successfully ran our Flash app inside Electron with an embedded Chrome 83 version
In email conversations directly with Adobe staff, I have confirmed you need to have a Flash licensing contract to legally distribute the Flash plugins in an Electron app. I believe it's always been this way and will continue to be.
However, Adobe is no longer the company to work with for licensing. Adobe has endorsed Harman as the Flash partner/maintainer going forward into the future. See https://services.harman.com/partners/adobe
If you connect with Harman, they can sell you a license that will allow you to distribute the Flash plugins in an Electron app ongoing into the future. They can also provide you a packaged browser (their own Electron app) that points to your Flash URL.