What did Gottlob Frege do after retiring during World War I?

After retiring during World War I, Gottlob Frege moved to Bad Kleinen in Mecklenburg.1

During this period, his personal views became increasingly reactionary; he developed an intense hatred for socialism and democracy, which he blamed for Germany's defeat in the war and the perceived shame of the Treaty of Versailles. His private diaries from the end of his life also reflected strong anti-Semitic sentiments, a loathing of Catholics and the French, and a belief that Jews should be expelled from Germany.1

Regarding his professional life, Frege had largely ceased creative work by 1903, though he did produce three essays on the philosophy of logic after the war. At the very end of his life, he briefly returned to the philosophy of mathematics, having concluded that his earlier attempt to ground arithmetic in logic was mistaken, though this final project remained unfinished and unpublished.1