I have a homebrew feat (a version of Durable) that grants Advantage on Constitution Ability Checks. In the Modifier section, the Modifier Type is 'Advantage', the Modifier Subtype is 'Constitution Ability Checks' and the Ability Score is 'CON'.
While there are no listed abilities that use CON as the modifier, if you take an ability such as Athletics and customize the Skill Stat Override to CON, it then shows Advantage, as expected. However, for any Custom Skills, setting the Stat to 'CON' does not do anything to show Advantage.
I have a homebrew feat (a version of Durable) that grants Advantage on Constitution Ability Checks. In the Modifier section, the Modifier Type is 'Advantage', the Modifier Subtype is 'Constitution Ability Checks' and the Ability Score is 'CON'.
While there are no listed abilities that use CON as the modifier, if you take an ability such as Athletics and customize the Skill Stat Override to CON, it then shows Advantage, as expected. However, for any Custom Skills, setting the Stat to 'CON' does not do anything to show Advantage.
https://www.dndbeyond.com/feats/664753-durable
https://www.dndbeyond.com/profile/MyDnDTestAccount/characters/26266364