This article's point of view is that although slipping in neutral with a manual transmission is not recommended, it is still possible and will not cause damage to vehicle or transmission.
Firstly, coasting in neutral is not recommended for vehicles with a manual transmission, but this does not mean that vehicle is moving on its own when idling, and this situation will not cause damage to vehicle itself or transmission itself.
Second, although above manual transmission vehicles may slip in neutral and vehicle and transmission are not damaged, this is not recommended for safe driving. Since slipping in neutral gear mainly occurs at medium and high speeds, and this is a habit of many people, especially when driving downhill, at this time, if car encounters an emergency, it needs to brake frequently and for a long time. , and braking must be reliable. Continuous and sufficient vacuum build-up, vacuum force generated under idle conditions is not as continuous and plentiful as vacuum force generated by gear coast motor, and gear coast motor can also generate braking force enough to limit vehicle's speed downhill, so it's still not recommended to coast in neutral.
I hope my answer helps you.
The above is just my personal opinion, feel free to comment/subscribe/like/.