see if python 3.9 fixes the copybutton

readthedocs.yml

@@ -5,6 +5,12 @@
 # Required
 version: 2
 
+build:
+  os: ubuntu-20.04
+  tools:
+    python: "3.9"
+    nodejs: 16
+
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
   builder: html
@@ -12,12 +18,10 @@ sphinx:
   fail_on_warning: true
 
 # Optionally build your docs in additional formats such as PDF
-formats:
-  - pdf
+formats: all
 
 # Optionally set the version of Python and requirements required to build your docs
 python:
-  version: 3.8
   install:
     - requirements: doc/requirements.txt
     - method: pip