Answer
The Notification Bell icon is related with Collaboration feature. If you want to disable the collaboration notification bell, it is equivalent to directly disabling the collaboration feature. You may disable the Collaboration Plugin inside pdf editor or use Foxit Customization Wizard tool to disable Collaboration Plugin.
1.Disable Collaboration Plugin inside pdf editor
1.1 Open PDF Editor, go to Help > Foxit Plug-Ins, a pop-up window for About Foxit Plug-Ins will appear.
1.2 Locate "Collaboration," turn off the feature.
1.3 Restart the pdf editor program, and the feature will be disabled.
2. Disable Collaboration Plugin by using Foxit Customization Wizard tool.
2.1 Open Foxit customization Wizard
2.2 Open the corresponding package.
2.3 Navigate to Plugins on the left panel and check the Collaboration as the screenshot.
2.4 Save the setting and apply by command line below
msiexec /i Setup.msi TRANSFORMS=xxx.mst
"Setup.msi" stands for the msi package you downloaded
"XXX.mst" stands for the .mst you configured and saved
Once it is disabled, the collaboration features as the screenshot related cannot be used
To download the correct Foxit customization tool, please refer to the article.