Applying the border visualStyle to an action button seems to add a second border in Power BI desktop June 2025, this second border seems to work independently to the one in the format button pane.
I can't seem to be able to address tileShape / rectangleRoundedCurve either, I'm using schema 2.144
"border": [
{
"color":{
"solid": {
"color": "#000000"
}
},
"width": 3,
"show": true
}

Applying the border visualStyle to an action button seems to add a second border in Power BI desktop June 2025, this second border seems to work independently to the one in the format button pane.
I can't seem to be able to address tileShape / rectangleRoundedCurve either, I'm using schema 2.144