Downgrade Node to 16.x would be fine for my app, but I don’t know how to specify a specific Paketo buildpack in the fly.toml 
The default in the fly.toml is gcr.io/paketo-buildpacks/nodejs and that requires node 18 and up.
Ok, I got it !
I looked up a buildpack that should work for node 16 and made a change in fly.toml to gcr.io/paketo-buildpacks/nodejs@sha256:26c7da06bc1fcb353f3357250d2735dad28396a39a2269b6cd99a0ee676844fa.
Ran the fly deploy --remote-only again and it picked up this buildpack, and the deploy went through 
Thanks a lot for pointing me in the right direction 