Requesting help with a very, very late perspective change.
As such I have been debating to give this new character their own chapters or parts of chapters, with the perspective changing to them and what they are doing. My question to people who are more used to reading than me, would this change come across as too jarring, when the perspective has staid consistent like this for the duration of the story?
I would instead recommend you do interludes. 1-2 "new chapters", then back to the old cast for a while, then 1-2 new ones, etc. Because I suspect most readers would be disappointed every time a chapter comes out and it doesn't "follow the main cast". It takes time and effort to connect with the new characters, and if they're reading, they're already "in love" with the old ones. So you need to make these "new chapters" amazing, they have to be way better than the old ones if you don't want the reader to feel betrayed. That's my thought process.
If you're using first, don't do it.
If you're using third, it can be done, but like Ararara said, don't just suddenly switch to just the new person.
Suddenly switching to the POV of a character without any apparent immediate connection to the existing cast would be an example of an opposite approach and is a difficult pill to swallow for readers -- it's basically presenting them with a new novel with a promise that it'll connect to the old one.
Then there's everything in between in terms of how connected the new character is to the old one.
In essence, I think most readers feel "committed" to a story because of its cast, so if the cast suddenly disappears then so does their reason to continue reading it (over looking for a new story). Of course there are exceptions with heavily plot-based or setting-focused stories, or ensemble casts.
Another suggestion -- the interactivity of web fiction gives you some extra options. You can simply warn your readers through author notes that you're thinking of introducing a new POV or ask them about it to give them advance warning. Then they're not blindsided and it might prevent some people from dropping the story. You could promise that the original characters will return in X chapters.
If I am reading a story of 20 chapters or more, I already have an inkling of your MC and sort of accepted him. If you add another dude... well, it kinda gives me the impression that the story is going off on a different path than the one I already have in my mind. So, no, I will not like that.
I've decided on a compromise where I will be doing split chapters, where appropriate, where the main half continues to center around the main character, and switching over when appropriate. I continue to feel that while somewhat sudden, it is a worthwhile addition and opportunity for me to also deliver on information that would be somewhat unfitting in the surroundings of the main character.
I keep the descriptions vague due to spoilers, but I can assure that the change is not without some prior establishment, and not a permanent one, as the two perspectives will ultimately merge a bit later in.