There should not be a ~ on the front.
So first check that running this in a terminal works (no ~) sudo /home/pi/fm_transmitter/fm_transmitter -f 102.7 acoustic_guitar_duet.wav
If it does then does it ask for a password?
Have you specifically disabled it for the node red user for that command or have you completely disabled password with sudo. If you have completely disabled it then I hope you realise the security implications of that.
An even better way is to give a particular user group access to whatever resources the command needs that normally requires sudo, then the node-red user would not need to use sudo with that command.
Haha, I did stress the if you really must part. Didn't say it was best, just that you can.
You can always use a credential and insert it to the flow data. That wouldn't be too bad, good enough for most things. I wouldn't have any exec nodes in flows that might be accessible from the Internet in any case.
I thought raspbian had stopped allowing sudo without password, but maybe it is only on raspbian lite that this is true, or maybe I am completely wrong.
In practice it probably isn't much of an issue as long as nothing on your network (in particular node-red) is accessible from the internet, or by possibly malicious users via the wifi.
Well, it is just a setting away even if they have. I've not installed a Buster version of Rasbian so I don't know myself.
I'm moving onto Debian Buster on an old(ish) Lenovo x240 laptop. I finally outgrew my 2 Pi's. The alternative was a 4GB Pi 4 but it wasn't worth the money for me. 8GB RAM and an i5 makes a nice platform and not too power hungry as it is a slim laptop with the screen off and set to low-power CPU mode.