Let me count, like 8, if I didn't forget one. Excluding one or two that are not really dedicated chat platforms but it's a 3nd class citizen.

discord unfortunately

I have a few, my misskey instance is the main one though, but I do have LINE, and XMPP as well.

Signal, Discord, Fedi(Kitsunes.Club/Kitsunes.Gay)~! All stay open on my desktop, though these days I don't use Discord nearly as often outside of contacts I have only available through there.

Twitter, Instagram, Here, and Twitch if it counts

From memory, 6. Most of them are listed here, and if one isn't, then it's not some contact info that I share with everyone.

discord & xmpp

Whatsapp, Facebook, Google chat, Discord, I'm also on a couple of Twitter wannabes, one of them on mastodon, I just don't use them

Signal, Discord, Matrix, XMPP (but nobody's messaged me in a while and I don't care), DMs on all the forum sites I use, SMS (because smartphone)

xmpp, matrix