Does that give us a little "taste" for the Dolomites even though we can't do any more than that?
I spent two months in Bolzano a few summers ago. It’s a beautiful city with mountains surrounding it on all sides. It has a very Austrian feel to it. Very nice, well-maintained city. From Bolzano you can visit the mountains of Renon (Ritten in German) by funicular as well as a few other mountains. I visited Colle (Kohlern in German) quite often, which is another mountain with beautiful views and a wonderful restaurant on top with amazing south Tyrolean food. You can get there by funicular on the edge of the city. If you have a car, you might also choose to visit Alpe di Siusi. It wouldn’t be too far from Lago do Garda if you have a car, and it’s absolutely breathtaking. That would give you a real feel of the Dolomites in my opinion! If you need any recommendations for places to see, restaurants, etc I am happy to share!
Yes do-able and imo definitely worth it for a day from the lake (you wouldn’t have much time to go further into the mountains if you want to explore the city.) I love Bolzano for its shopping and unique feel - and the drive from the lake is beautiful with castles you can see from the sides of the autostrada. If you had a few more days there it would allow you to drive further into the dolomiti for hiking.
Trento is also a great day trip from lago di Garda - shorter drive than Bolzano but also gives you a taste of the region. These two cities were two of my favorite day trips from the lake when we lived there.