Is this what you're looking for?

here's what i had to set to make this work:
Gallery:
- 'Default' property = DefaultSel
Play button:
- 'DisplayMode' property = If(DefaultSel.Name= ThisItem.Name, DisplayMode.Disabled, Edit)
- 'OnSelect' property = UpdateContext({DefaultSel:Gallery2.Selected})
Pause button:
- 'DisplayMode' property = If(DefaultSel.Name = ThisItem.Name, DisplayMode.Edit, Disabled)
- 'OnSelect' property = UpdateContext({DefaultSel: {}})