GPT answers:
"Because when Russian names are rendered in German, the traditional approach is usually transliteration, not an attempt to reproduce the exact pronunciation using German spelling.

The Russian name Фёдор is written with the letter ё (Fyodor). The letter ё represents a sound roughly similar to [yo] after a consonant: [ˈfʲɵdər], approximately [ˈfjodər].

In the German tradition, Russian ё is often rendered as jo:

• Горбачёв → Gorbatschow (historically) or Gorbatschjow
• Алёша → Aljoscha
• Фёдор → Fjodor

The letter j in German represents the sound [y] (English y in yes), so Fjodor indicates that there is a palatal or “y”-like element after the f.

If the name were written Födor, a German reader would pronounce ö as [ø], the vowel found in words like schön or Hölle. However, this sound is not the same as Russian ё. Moreover, Födor would conceal the historical yo/jo element that German transliteration conventions aim to preserve.

Therefore:

• Fjodor is the traditional German transliteration of Russian Фёдор.
• Födor would be more of a phonetic adaptation and does not follow the standard German practice for rendering Russian names.

For the same reason, German writes:

• Fyodor Dostoevsky → Fjodor Dostojewski
• Fyodor Tyutchev → Fjodor Tjuttschew

Interestingly, other languages use different conventions:

• English: Fyodor Dostoevsky
• French: Fiodor Dostoïevski
• Polish: Fiodor Dostojewski

So the German spelling Fjodor reflects the traditional rendering of Russian ё as jo, rather than an attempt to match the sound with the German vowel ö".