Internal browser is needed, especially for YouTube links.
I appreciated how the reddit app I used (relay) kept everything internal. I don't want all the links I open on this app opening in my browser and plugging up my history. I doubly appreciated how it would open YouTube links in an internal video player that wasn't linked to my YouTube account in any way. This is a must have for me to prevent my YouTube "algorithm" from getting any ideas. For example, I watch a video about "X" and now my whole feed is suggesting I watch more videos about whatever "X" was.
On the other hand, an embedded link viewer has no uBlock and other extensions/privacy settings as my browser does. Id rather just open youtube in forefox.