Copying and pasting a paragraph from here:
The rules of origin requirements are some of the most important provisions that your business needs to understand and meet, under the UK's deal with the EU.
www.gov.uk
doesn’t exactly smack of a deep understanding of the issue. In fact your post demonstrates the opposite. The page from which you have copied also says this:
“To export tariff-free under the TCA, goods must meet the UK-EU preferential rules of origin. This means that there must be a qualifying level of processing in the country of export to access zero tariffs.”
In other words, unless goods and all of their constituent parts have been wholly sourced in the EU or UK, or been subject to significant processing, then they will be subject to tariffs. That conditionality and the complex rules attached to it mean that this tariff free deal isn’t tariff free for a huge proportion of businesses in the UK.