There is no evidence in this as Omer may Allah be pleased with him was
showing them not to prolong the bowing and prostration. His sitting
position was not necessarily included in his display.

Either way, it is not a serious issue and it is disputed upon scholars. One
can take what he feels is closer to the sunnah.

I read in a book: There’s no hadith to prove not to do Tawarruk in tashahhud of 2 rakat prayer but a hadith that suggests otherwise, in Musnad alFarooq and Khilafiyat alBayhaqi which says (part of hadith): ثم صلي رکعة اخري مثلها ثم استوي جالسا فنحي رجليه عن مقعدته والزم مقعدته الارض ثم جلس قدر ان يتشهد بتسع کلمات ثم سلم وانصرف