Hello @AlwaysHappy
I know this is quite some time later, I experience both depersonalisation and derealisation. There is a podcast called Traumatized Motherfuxxers. I understand that the name might be off-putting. The young woman who runs the podcast tends to come at these forms of dissociation from an academic and lived experience background. I have found her podcast immensely helpful. For most of last year I thought that my depression was ramping up. It turns put it was a slightly different form of derealisation which was explained at length in one episode. She also provides what has worked for her in the past, or is working for her in the present. I was only able to access the podcast through Patreon because i use Android rather than iPhone. From some of the stuff she says it sounds like her podcast is available for free on an Apple podcast app.
Something else that really helped was a medication that I'm not allowed to type here, at lunchtime. The med sounds like quiet in a pine forest. The worst of my disappearing was in the afternoon. I don't know how that worked, and it's definitely off label, but it really worked for me until I was able to get a handle on things myself. One of the things that helped me get a handle on this stuff was committing to the bi-lateral stimulation part of the EMDR therapy with my psychologist. Going through some of those memories has been terrifying and really grounding.
Can't think of anything else this late at night. If more comes to me I'll post about it. Hope the young person has been able to get a handle on this stuff. Cheers