Traveling by car Munich to Soelden Austria
 

Checked google maps for routes to drive Munich to Soelden Austria- we will be driving December 21. Wondering what most scenic route is, as travel times aren't too different. Driving back to Munich, we will be fine taking the fastest route. Thanks!

https://www.viamichelin.com/ gives you the option of specifying fast route or scenic, among other choices.

The "fastest" route, i.e. mostly via motorways, can be the slowest.
From Munich, Google will probably tell you to go via A8 to Rosenheim, S on A93 to Kufstein and then along A12 until you get a bit W of Innsbruck. This route is THE major artery to the South.

While Dec 21 will be one to two days before the exodus from Bavaria and elsewhere to the Alps starts, I would check Google again on Dec 21 with the traffic layer activated.

If traffic is okay, the route via Kufstein will incur an extra 9 or so euros for the motorway vignette in Austria.
If you don't plan to drive anywhere else in Austria but Munich-Sölden-and back then the vignette is a (moderate) waste of money.
As you don't need it.

Munich - A95 S
exit 9 (Sindelsdorf)
few kms E on B472 until you hit B11
B11 S to Krün
B2 W to Garmisch
B23 W to Lermoos (Austria)
B179 S to B189
B189 W to Imst
B171 E to Ötztal highway (B186)

It sounds more complicated than it is.

P.S. Road signage does not feature "west" or "south" in Germany or Austria.

Thank you both for excellent trip planning advice!