Error when I try to download an addon

I can’t install any addons, I receive a message saying there is an error

Perhaps the add-on does not support your installed Anki version? Please provide detaills about which add-ons in particular you are trying to install and the verison you are using and the error message that pops up.

I am trying to install the heatmap and the progress bar
my anki version is 2.1.26windows

the error message is the following:

An error occurred. Please start Anki while holding down the shift key, which will temporarily disable the add-ons you have installed.
If the issue only occurs when add-ons are enabled, please use the Tools > Add-ons menu item to disable some add-ons and restart Anki, repeating until you discover the add-on that is causing the problem.
When you’ve discovered the add-on that is causing the problem, please report the issue on the add-on support site.
Debug info:
Anki 2.1.26 (70784154) Python 3.8.0 Qt 5.14.1 PyQt 5.14.1
Platform: Windows 10
Flags: frz=True ao=True sv=1
Add-ons, last update check: 2020-07-08 09:58:39

Caught exception:
Traceback (most recent call last):
File “C:\Users\paula\AppData\Roaming\Anki2\addons21\1722241614\libaddon\gui\basic\”, line 93, in accept
File “C:\Users\paula\AppData\Roaming\Anki2\addons21\1722241614\libaddon\gui\”, line 130, in _onAccept
File “C:\Users\paula\AppData\Roaming\Anki2\addons21\1722241614\libaddon\anki\”, line 216, in save
File “C:\Users\paula\AppData\Roaming\Anki2\addons21\1722241614\libaddon\anki\”, line 457, in _saveSynced
self._getStorageObj(“synced”)[self._conf_key] = config
File “lib\site-packages\anki\”, line 60, in setitem
File “lib\site-packages\anki\”, line 36, in set
File “lib\site-packages\anki\”, line 591, in set_config_json
orjson.JSONEncodeError: Type is not JSON serializable: WrappedDict

Another user reported the same problem before. I guess you are not using the most recent version of the add-on which may not be compatible with 2.1.26.