Node-RED is really tough for Bun to support because it relies on sloppy mode features like implicit global variable assignment (assigning a variable without var/let/const) and Bun currently treats every file as ESM (and transpiles CJS for compatibility)
For Bun on workflow builders, I'm currently working on making windmill [1] supports bun as an additional runtime to run the typescript scripts/steps. It's not the same as making the workflow engine run with bun (we use Rust) but I thought it might be worth mentioning :)