I guess we need to wait for someone else to chime in, but as I understand it, there is no “transaction fee” for converting XTM to XTR. The transaction fee is being paid to the validators for transactions happening on the Ootle. No valiators are needed to oversee the burning of XTM to XTR.
That whole paragraph you are quoting is a bit misleading in its wording as it commingles two different processes: the minting of XTR and the transactions on Ootle. And both have a component of “burning”, though only one of those burns ultimately removes tokens from the supply.
I would also like to reference the image from the Tokenomics page again:
The “A % of all transaction fees is burned” happens between “Tari L2” and the Tapps, not between “Tari L1” and “Tari L2”.