Product update webhook – what does / does not trigger it?

We have a setup on our store whereby we store a custom price for visitors to a certain locale in a variant metafield. Occasionally, our team may input an incorrect value.

We’ve created a system that uses the ‘Product update’ webhook to notify us on Slack if a value is entered that falls below a target GPM. This seems to be working nicely, however we’ve noticed the webhook behaviour appears to be a little erratic, and trying to understand how it works.

It seems to fire when an order is placed with that product in it, presumably because the inventory levels are updated. It also fires if fields like the product description are updated. However, updating the variant metafield does not seem to trigger it – according to this thread, this appears to be a known ‘issue’: Webhook product/update not fired after variant's metafield is changed - Shopify Community

I wanted to check:

1.) Is what is discussed in the above thread correct – i.e. variant metafield updates will not trigger?

2.) Other than updating a ‘core’ product field, or placing an order, are there other conditions that will trigger?

Thank you in advance.