As listed in our article How do we control who can access and use Design Tools? hiding the Design Tools launch button but leaving the Multi Tool and Upload/Embed Image Tool available is a popular option.

To do this, you will need to access your global JavaScript.

In your global JavaScript file, there is a line that says:
    hideButton: false,
Just change that to say:
    hideButton: true,

It is typically the 11th line down within the Design Tools portion of your JS.

Upload the updated file to Canvas. This will require users to know one of the two keyboard shortcuts to get into the rce sidebar tools.