'Secret'?
Huawei's breadcrumb trails are pretty easy to follow, if you really want to follow them, and the admission by SIA that it based its claims on publicly available data (which no doubt included a slice or two of speculation) shoots a big hole into the 'secret' aspect of all this.
Huawei, like Apple, Google, Microsoft and practically every other tech company on the planet does have labs, research centres and the like which contain 'secret' products etc but you can't keep mass production sites secret at all when the products are destined for the consumer industry.
The manufacturing 'grey' market for some manufacturing tools (hardware and software) has always existed. Getting things from that market or 'second hand' is commonplace across all industries, too.
Let's not forget that both China and the EU have 'sanctions busting' laws. AFAIK, China has only used those once since sanctions began but if a Chinese company can legally purchase US technology, Chinese law makes it very difficult for them to not be able to sell it on within China.
The US is well aware of this.
As for Huawei's plans, well logically they don't advertise them and, under the current circumstances, they even go out of their way to 'openly' keep some things 'secret'. That's why all the circuit boards and chips on show at MWC2023 were taped over or eliminated.
What are they doing exactly with regards to chip manufacturing?
No one on the outside knows officially, but it is clear they have no alternative but to become vertical in chip production as soon as possible.
They will do that through their own resources, government funding, common strategies with universities and by investing in local technology companies and pushing them to improve their products.
The 5G BAW-filter 'choke point' is a rumoured clasic example of this.
The US openly spoke of destroying Huawei. It used the term 'choke' on many occasions.
However, It looks like it is the entire US semiconductor industry will end up choking on the sanctions in the longer term.