I’m voting for Biden because I don’t want Trump picking the next couple Supreme Court justices.

Not only could he pick the next ones, he would have the power to expand the Supreme Court. Imagine a SCOTUS that isn’t just filled with Federalist Society goons but his own special brand of Conservative from places like the Fifth Circuit in Texas.

Pardon my ignorance as a non-American, but weren’t there rumblings of Biden being able to do the same, back around the time of the RBG debacle?

Yep, and he didn’t out of some misguided belief that Republicans would behave with some amount of human decency. Unfortunately, the Republicans he knew from his time as a Congressman had given up decorum and bipartisanship for their personal ideologies and fealty to a fraudster.

It would have been and still is the sensible thing to do, because the highest judiciary should be the least partisan, and it’s a progressive move Biden really should make in an effort to maintain that balance.