I don't know, and I don't believe it's possible to know in a specific instance. Like I said above, I believe that in the long term, denser towns raise the property values of their suburbs by making the area more desirable.
But there is definitely a plausible case that increasing the supply of housing immediately lowers or slows the growth of property values by reducing scarcity. It's the argument made by both sides of the "missing middle" debate in Arlington -- the pro side says it will make housing more affordable, and the con side says it will lower everyone's property values. The article we're commenting on found that at least some version of this is true for the Austin, TX -- increasing housing stock lowered rents, even if the new stock is luxury units.
Also agree it's difficult/impossible to know for a single piece of real estate. And impossible to know for sure since the market is complex (impacted by rates, other policy decisions, etc)
The most overt statement of "we don't want to build more houses because it will decrease the value of existing houses" in recent memory was Trump[1], who is not exactly a reliable source (and whose whole brand prior to politics was destroying the character of established neighborhoods by building giant condo complexes).
[0]: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=5780364 [1]: https://www.msn.com/en-us/money/general/trump-says-the-quiet...
But Falls Church is much nicer now that a few mid-rise apartment buildings with ground-level retail have gone in! As a resident, I am very happy about all the new development. I expect that over time, that will have a positive effect on property values, but there is an observable short- and medium-term effect working in the opposite direction as the increased housing supply eases demand on the existing housing stock.