> Modal windows can't be bookmarked or shared as links
Why would the user want to bookmark or share a "modal". I believe the author is confusing a modal with a details page (a customer's details page in a CRM for example) on that we can agree that that kind of content is best shown on a separate page. A modal serves a specific function within a web page, be it a website or a web app. Its main function is to allow the user to perform certain tasks within a page, and those tasks will immediately reflect on the underlying page upon submission (or validation/confirmation ..etc). So I fail to understand why the author thinks a user would want to bookmark that modal.
> Modal windows can't be opened in a new tab
Nor should they. Modals, as mentioned above, are one layer above an underlying page, and they either show complimentary information related to an element within that page, or they allow to user to performa task. So they should inherently be accessible within the same tab, not a new one.
> Modal windows make the Back button confusing
Aside from the Close/Abort button inside the modal, a lot of interaction designers and front-end developers are now developing the modals in a way they would close if you press the back button of your browser. No confusion there in my opinion.
> Modal windows are hard to get right[...]if you need to support older browsers, good luck.
Can't find the date this article was published but I assume it's old because almost all new browsers support at least <dialog> element [1]
Modals are a double edged sword, like any UI component or UX pattern really.
[1] https://developer.mozilla.org/en-US/docs/Web/HTML/Element/di...
Further reading: https://www.nngroup.com/articles/modal-nonmodal-dialog/