I'm wondering a bit how this question is not an exact duplicate of Are Component Links supported for inline edit in XPM? but I guess since you are asking it based on DXA 1.8 and SDL Web 8.5 the answer could have been different.
Unfortunately as I stated in my answer at the previously mentioned question, to support inline editing of Component links in XPM, one of the following things need to be changed:
a change in XPM where it is possible to edit just a Component and not only Component Presentations
a slight hack in DXA for editing linked Components, by using a dummy Component Template URI (this would be a real Component Template URI, which is only used for editing linked Components)
Now if you check the release notes of SDL Web 8.5 (which came out before DXA 1.8 was released by the way, and also before I wrote my answer, so you can guess where this is going ;o), you will notice that the change in XPM as suggested in #1 isn't there (I don't even think it is on the roadmap, so don't hold your breath till the next release, as it most likely won't be in there either, you might want to submit an idea to get attention to it).
Next you can check the release notes of DXA 1.8 and in there you will notice that the change as suggested in #2 also isn't available in there.
So that sums up that the answer to your question is still the same as my previous answer. I can add, that Andreas Rönnqvist has been so nice to supply more details on the slight hack, I mentioned in #2, in his answer. You might want to check that out.