Was originally going to dispute the first paragraph, but @Euphonious_Polemic did a really great job of that upthread, so I’ll continue on to the rest.
This isn’t about, or even Needing mass arrests, or even the short term detention @Euphonious_Polemic suggested. All it has to do is make people avoid showing up to vote because they’re afraid of being arrested, harassed, or otherwise punished. If they don’t show up to vote, accomplished without said arrests.
As for mail-in-voting, states that still allow it are mostly blue write offs anyway. No need to worry there. It even helps with the point of keeping the appearance of fair elections. Trump or his stand-ins aren’t going to win in deep blue states anyway, and that way he always has someone to blame. As long as he minimizes risks in potentially winnable states for (D) it doesn’t matter.
If that’s all, then I’m not sure if this ruling actually made a difference. I don’t think Trump needed this ruling to be able to do “just” voter intimidation without actual arrests. I’m sure that if you get a tape measure out, you could easily figure out the minimum distance to technically stay within existing law.
In and of itself, no, it’s not making a large difference in terms of voter suppression - though I’m sure there are people who are now more afraid and hesitant which is still a win for their side.
Rather, it is a part of testing how far the courts will let him go (there have been a few times the SCOTUS didn’t give him everything he wants after all), and building ever more tools to accomplish the net autocratic/MAG oligarchy goals.
It’s still bad law, bad precedent, and one move shovel-full of earth into the grave of actual representative American government.