The Flume trail is just great for the views and still pretty fun. If do you an out and back there's a lot of climbing to get to it, but it's otherwise non-technical.
However, you can also take a
shuttle from Spooner Lake to the Tahoe Rim Trail trailhead on the Mount Rose Hwy. This is not a shuttle to give you ripping downhill, but simply makes ride a bit easier and lets you go a little further. The Rim Trail has some slightly technical bits and there's still some climbing, but I've done it with beginners before without issue. The views on the Rim tTail are great too and then it leads to the Flume Trail where it gets better as you're able to look down into blue water around sand harbor. This is good option for someone you're trying to get into mountain biking.
Emigrant trail is also a good beginner trail. Can be a bit dusty and views aren't as great, but ride is nice.