“When Tiffany takes Duffy’s seat Governor Evers will be appointing his successor.”
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Huh? That’s not how state-senate vacancies are filled in Wisconsin. Check this out, from the “How vacancies are filled in state legislatures” page on Ballotpedia:
Wisconsin
If there is a vacancy in the Wisconsin State Legislature, a special election must be held to fill the vacant seat.[96] The governor can call for an election when allowed by law. The election cannot be held after February 1 before a spring general election, unless it is held on the same day of the election, which is the first Tuesday in April. The same requirement applies to any election preceding the fall general election (after September 1), with the exception of elections held on the first Tuesday in November.[97] Also, all vacancies must be filled quickly as long the vacancy happened before the second Tuesday in May during an election year.[98]
See sources: Wisconsin Cons. Art. IV, § 14
https://ballotpedia.org/How_vacancies_are_filled_in_state_legislatures
I don’t think any state has a Governor fill vacant state leg seats by appointment, unless maybe it’s appointment by a list selected by the outgoing members party, like Wyoming does for US Senate vacancies.
In Illinois party bosses get to make the appointment.
Most states just have special elections.
This is complicated by the election dates and the date the final winner of the 7th Congressional Dist WI seat is sworn into office which is January 2021.