You can go about this a few ways.
The simple approcah is:
In the button's Visible control field:
If(Dropdown.Selected.Value="Text from Dropdown 1", true,false)
Perhaps you need to create another list to assist you in your rules. You can compare values without the need to keep adjusting the syntax, it a lot more managable.
Then you can create syntax on a filter to show the button.
Create another list for example with 1 column, then create a collection from that. Collect(ButtonKeywordsCollection,'ButtonKeywords')
Title: ButtonKeywords
Now on the buttons Visible control field:
if(Dropdown.Selected.Value = Lookup(ButtonKeywordCollection,Dropdown.Selected.Value = Column1,Column1,true,false))
if(Dropdown.Selected.Value || Dropdown2.Selected.Value = Lookup(ButtonKeywordCollection,Dropdown.Selected.Value = Column1,Column1,true,false))
This syntax may be different from SharePoint list and an excel sheet.
You can come up with methods like this is you think inline syntax will get too unmanageable.