advocacy threat- tax computation

Not really - "mere" tax computation is routine - and gives rise to self-review threat (because the tax liability is in the SoFP). Advocacy threat would arise if, for example, client is already in dispute over a tax treatment and asks auditor for advice to support their position - or if the client asks the auditor to advise on an accounting treatments or tax schemes that would avoid tax.

The preparation of the tax computation ALONE does not of itself create an advocacy threat - there is no "advocacy" to anyone. It is the completing the company's tax returns (as per scenario) - suggests potential advocacy threat.

But any tax return will generally be submitted with a declaration of the factual accuracy/completeness of the return and where it is submitted by a "representative" of the tax payer, the representative will be named.

I am trying to justify the answer you quoted as it comes from the examining team. That said, having looked at the Code again to answer this post https://opentuition.com/topic/ethics-34 I am of the opinion that my first response was correct and that the answer you quote is "over egging" the advocacy risk.