It seems like you have to use one of the pre-installed ringtones in order to have vibration, at least that’s the case on my Nothing Phone (2) since at least OS 2.6
For example using “ripple”, the phone vibrates, selecting a tone I just composed using the Glyph Composer: No vibration. Selecting another random custom ringtone: No vibration.
I opened a support ticket a while ago and was basically vibration only works with factory ringtones on OS 2.6