What do I serve with an apricot-berry tart? For brunch?

Unsweetened whipped cream

I was thinking AS caetie greek yoghurt and a fritatta

If available in your area, I would go for simple grilled fish (trout with lemon and herbed rice, or what's best in market) as main dish.

Some plain greek yogurt would be great as a toping for the tart. If you're looking for additional dishes, I would say poached eggs over greens or a frittata.

It would be nice to take advantage of summer veggies along with those wonderful fruits. I like to make a light summer succotash with poached or sunny side eggs. Things like zucchini, sweet corn, butter/fava beans, romanesco, shallot, etc. You could toss in some farmer's cheese and light herbs like dill and chive....fresh and not overpowering in the least.

Sounds wonderful. I would just provide something basic like slices of ham and scrambled eggs.

I'd make tartine with lentils, braised greens w/bacon and a poached egg.