Vaadin and IE11
Vaadin 14 kinda supports IE11, but there are limitations. The performance hit is substantial, for example vaadin-grid may perform 5x-10x slower in IE11 than in Chrome or Firefox, on the same machine. This performance hit will not be fixed (it can not be fixed) - if you need a performant site for IE11 then Vaadin 8 is the best choice.
Vaadin 15+ does not support IE11 and will display the following page:
An excellent way to test this is to take advantage of the browserling.com page which will launch IE11 in a VM for you. For example, here’s the https://labs.vaadin.com/business Business Starter running in IE11 on Win7.