I had formerly been definite about the former, following al-Haythamī, in my book Takhrīj Ṣifat Ṣalāt al-Nabī (Documentation of the Prophet’s Prayer). Then I came to withhold judgment on the matter because of the investigation I have mentioned.

Yes, the hadith has another chain from Ibn ʿUmar by which it is strengthened. Suraij ibn Yūnus narrated to us: Qurān ibn Tammām narrated to us, from ʿUbayd Allah ibn ʿUmar, from Nāfiʿ, from him, that he said: The Messenger of Allah, may Allah bless him and grant him peace, said:

“Whoever among you is able to prostrate, let him prostrate. Whoever is unable, however, should not raise anything to his forehead upon which to prostrate; rather, he should gesture with his head for bowing and prostration.”

Al-Ṭabarānī recorded it in al-Awsaṭ (1/43/1—among its supplementary narrations): Muḥammad ibn ʿAbd Allah ibn Bukayr narrated to us: Suraij ibn Yūnus narrated it to us with this chain. He said:

“No one narrated it from ʿUbayd Allah except Qurān, and Suraij alone narrated it.”

I say: He is trustworthy and among the narrators of al-Bukhārī and Muslim, as are those above him in the chain, apart from Qurān—whose first letter bears a ḍammah and whose rāʾ is doubled. He was truthful, though he sometimes erred, as stated in al-Taqrīb. Thus, the chain is good, were it not for the fact that I have found no biographical entry for Muḥammad ibn ʿAbd Allah ibn Bukayr, al-Ṭabarānī’s shaykh. Yet it appears that he was not alone in narrating it, as is indicated by his statement, “Suraij alone narrated it.”

Perhaps this is why al-Ḥāfiẓ al-Haythamī said (2/149):

“Al-Ṭabarānī narrated it in al-Awsaṭ. Its narrators have all been declared reliable, and none of them has criticism that would impair him. And Allah knows best.”