Collabora Online configuration troubles

on Nextcloud 18.07 (webhosting) I don’t seem to be able to get going with Collabora Online (I’m looking at and finding it a bit cryptic):

when I click on a word.doc I’d like to share, I’m told that I need to configure Collabora Online (screenshot 1). I click on the link provided, and I’m given three options, except that the one in the middle (“use the built-in CODE”, etc) is not clickable (screenshot 2). The link at this option is clickable, except that the “built-in server” I’m supposed to install is not available / not available in my app list.

Can you please advise - particularly regarding the possibility of “using my own server” as an alternative (webhosting), i.e., what I need to tell my webhosting provider. Thanks.collabora online 1