Is "adding real value" actually a criterion for something to be considered a capital improvement for rental property?

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@SKjames wrote:

.....Is this wording about "adding real value" actually listed anywhere official or is it just an unofficial litmus test used by many rental property owners?

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No, that wording is not listed anywhere; it was simply coined by another member of this Community and is unofficial (as opposed to the following):

An expense is for an improvement if it results in a betterment to your property, restores your property, or adapts your property to a new or different use.

https://www.irs.gov/publications/p527#en_US_2020_publink1000219015

There is no requirement that an expense "add real value" to the property in order to be considered an "improvement". Although many (if not most) improvements do result in an increase in the value of the property to which they attach, there is no requirement that they do so.

Actually, it's "add or maintain value" in a property.

Sometimes it can be difficult to differentiate between a repair and a property improvement. For example, if the fan motor in the outside A/C compressor burns out and you pay to have that fan motor replaced, that's a repair because The expense was incurred to return the compressor to the same usable condition it was in, prior to the event that caused the central A/C to be unusable.

However, if you instead elected to replace the outside compressor unit with a complete new unit, that's a property improvement. There's no doubt that a "new" unit will fetch a higher price for the property, than you might get with a 10 year old unit still there; even if that 10 year old unit had a brand new fan motor in it, the unit is still 10 years old.