Hello, Even though the post is a bit old, if it can help, here's a potential solution that I was able to test:

Create a JS file with the following content:

odoo.define('invoice_kanban.invoice_kanban_view_handler', function (require) {
    "use strict";

    var KanbanRecord = require('web.KanbanRecord');

    KanbanRecord.include({
        //--------------------------------------------------------------------------
        // Private
        //--------------------------------------------------------------------------

        /**
         * @override
         * @private
         */
        _openRecord: function () {
            var invoice_id = this.id;
            var self = this;
            if (this.modelName === 'account.invoice') {
                this._rpc({
                    model: this.modelName,
                    method: 'get_formview_id',
                    args: [[invoice_id]],
                })
                .then(function (view_id) {
                    var action = {
                        type: 'ir.actions.act_window',
                        name: 'Invoice',
                        res_model: 'account.invoice',
                        res_id: invoice_id,
                        views: [[view_id, 'form']],
                        domain: [['id', '=', invoice_id]],
                    };
                    self.do_action(action);
                });
            } else {
            this._super.apply(this, arguments);
            }
        }
    });
});

Don't forget to load it.

Odoo will then load the 'account.invoice_form' view instead of 'account.invoice_supplier_form'.

Hoping this will help others in the future.

Maxence

I did this:

1. Accounting --> Customers --> Invoices

I don't see "View Activity" so I edited the Invoices View and added the Activity View:

But when I use this View, I am not shown the Vendor Bill Form View, but the correct Customer Invoice form.

Can you confirm what the next step is after you reach the Invoices List View?  What do you mean by "View Activity"? 

I cannot find a Menu, button, filter, or other option to click or select "View Activity" - perhaps you have a customization?

I don't know what sequence to follow to "open Activities" into the Kanban View.  When I open Activities from the clock icon and the Kanban that follows, they open as expected:

When I add Invoices to my dashboard, they also open fine in the Customer Invoices Form View.

If you can replicate this problem via Runbot, then you can log a bug, as long as you provide steps that our team can follow to replicate the bug.  Screenshots or even a video make replicating easier as we can do exactly what you show us via those visual documents.

https://runbot.odoo.com