Thanks Rocco!
First of all, it seems that this menu in Yoast has changed in latest versions, but there is still a link under Yoast SEO -> Search Appearance -> General titled “You can determine the title and description for the front page by editing the front page itself”.
Problem here is, in my case at least, that I didn’t have any “front page” page at all because the Customize menu allows you to create your homepage with different elements, such a slider, without having a page defined as “homepage”.
So, what happens in such situations is that this link at Yoast doesn’t work and does absolutely nothing!
But I just found this discussion in current forum and this post from plugin’s author that seems to say that this is a bug that will be corrected. I’m not sure what exactly the bug is and if this has been corrected since then, but it still doesn’t work in my case, with both, plugin and theme, running in latest versions.
Unfortunately, this thread is now closed and this is really a shame as we could follow up there. BTW I really don’t get it why such threads are closed so early, with the last post in there being 8 months old!
But I read this last post in there and it solved my problem: I kept settings in Customize as they were and I just added an empty page titled “home” that I defined as “homepage” and then was able to set a meta description for it. My homepage remained exactly identical after this addition.
Hope this might help others in similar situation.