They basically are. They speak Russian and act like Russians. I doubt they'd mind being annexed.
They don't have russian passorts. How can they be russians?
You clearly are not familiar with how things work in Transnistria.
Just because Putin says those people are Russians so he can claim some clay, doesn't make it a fact.
Sure some are ethnically Russian, but that doesn't make them Russian citizens.
They are Moldovan citizens. Transnistria is a rouge separatist nation that's not internationally recognized and only exists on paper because Russia has troops and weapons there and Moldova is too weak to do anything about it.
Not sufficiently familiar then.
"It is estimated that about 250,000 out of 500,000 people living in Transnistria hold Russian citizenship."
That's as of 2020, "passportization" has continued since then.
https://warsawinstitute.org/russia-hands-passports-diaspora/
Case in point, no other UN nation recognizes Transnistria or Transnistrean passports. Transnistrean citizens travel with Moldovan passports.
All a Ukrainian invasion of Transnistria would do is give Putin's claims about Ukrainian aggression some veneer of legitimacy and annoy Moldova, which doesn't want to see something which is constitutionally part of their territory fought over and then bargained back to Russian control...