The adblocker is “Defender” on Chum, see Defender is back!
One native client for Signal is “Whisperfish”, see Whisperfish - The unofficial SailfishOS Signal client
I am not sure as I don’t have my J2 yet, but I guess from Jolla Store you could remove it.
However technically it is not Microsoft crap, but a Jolla compatibility layer with Microsoft crap servers. It is safe to leave, it won’t communicate with said Microsoft crap servers unless you configure an account.