Does vaccination status play into the equation? If vaccinated, or vaccination is expected by the travel date, then making a connection shouldn't present that much of an increased risk versus flying non-stop.

The OP's travel is planned for June. Things may be very different then in terms of lounges being open. Certainly with the recently announced lifting of travel restrictions for Americans entering the EU, there will be an increase in traffic TATL. One should also expect adjustments to the timetable, so looser connections provide more of a buffer against such changes.

VIE is nice because the airport is so small and efficient. ZRH is only a tad less efficient, and the non-Schengen lounge is marvelous with its outdoor patios and stunning views, even without food and beverage. FRA can take a substantial amount of walking to transit, if there are any issues around mobility. At least one lounge there (and I can't remember which) has a very nice sleeping space that is useful for a quick nap when arriving TATL.