Electron may no longer be an option. As per their page, https://www.electronjs.org/docs/tutorial/using-pepper-flash-plugin:
Electron no longer supports the Pepper Flash plugin, as Chrome has removed support.
See Chromium's Flash Roadmap for more details.
Also, Electron embedded the Flash Player plugin which requires a distribution license to do.
"Then is there a safe way to keep our Flash applications in our portfolios in the future?"
The best option is to migrate to a different technology, as recommended over 3 years ago when Adobe, and all browser vendors, annouced Flash Player's end-of-life:
For enterprises dependent on Flash Player, please refer to the Enterprise end-of-life FAQ:
Enterprise Enablement may be an option until such time all browser’s remove support for Flash support. Technical details can be found in the Flash Player Admin Guide, pages 28-35):
Google Chrome & Apple Safari have removed Flash Player support (Chrome 88 and Safari 14, respectively). Firefox will remove Flash Player support in Firefox 86, scheduled for release Jan 26, 2021. See End of support for Flash Player