Joining two different-widths PCB traces
no etching problems?

If the smaller width works, this will also not be an etching issue. Also, this is a DC line, so you don't have to worry about anything geometrically here.

elegantly

You're asking about æsthetics here. Well, can't help you with that, honestly, different people find different things pretty. It might be prettier to simply not have the thicker line extend this far up, so that the rounding doesn't extend beyond the upper edge of your thinner trace.
But honestly, go with what you layout software does.