Nothing has changed here since TSW. You can choose a 4k Resolution but you will end up with half of a working UI. Some Elements are not scalable at all, some Text and the chat are unreadable.
In a time where even Consoles are getting 4k this is a sad thing and I hope that Funcom will work on that topic soon.
However, there was a method to upscale things in TSW, an Addon for 4k Support which fixed some things. I never tested it and don´t know how it worked and we did not have access to the api during the beta, that´s why I can not say if Addons which worked in TSW will work in SWL. I did test one and it worked fine, but it was a simpler one.
Someone in the Forum mentioned that it is still possible to scale things by changing values in the UI config files. This was done by some players with TSW before. I did not write down the code he provided, but I am pretty sure this will find the way to reddit and the official forums.
No other choice than to wait and to hope for the best.