Modules in admin showing 404 not found

I’m having trouble getting some modules to work.

I installed 2 modules on a clean magento 2.3.3 version.

The modules are a theme and an extension that switch to maintenance mode.

Whenever I do some changes to apply one of those modules, I get a 404 not found page.

I did notice that the URL in both cases shows a key like this :

https://website.com/adminpage/theme/design_config/save/key/######

https://website.com/adminpage/maintenancemode/adjustsettings/save/key/####

The numbers are different on each url.

I installed those modules with the following method :

php bin/magento setup:upgrade

php bin/magento setup:static-content:deploy -f

php bin/magento cache:clean

“Add Store Code ” is not activated (according to an other post it should be that way).

Any idea how to fix this ?