There are many territorial disputes that are ongoing.
At this link is a long list of them.
One example: Hans Island claimed by both Canada and Denmark. At the link is a map with a many dash line on the surface of water at a place called Kennedy Channel.
China does not argue (present tense) anything in relation to BDTCs, because (for the purposes of this discussion) they no longer exist. Everyone who held BDTC status in relation to Hong Kong lost it on 1 July 1997.
It is difficult to speculate on the exact course of Sino-British negotiations leading up to the handover in 1997. However, it seems plausible ...
On a legalistic level, I do not agree that granting British citizenship to the people of Hong Kong constitutes a violation of the Joint Declaration, or is an interference in Hong Kong's affairs, because citizenship and nationality are purely internal matters. Who is a country's citizen or national is determined solely by the law of that country, and what it ...
The Institute for Government has published an explainer on this, the most relevant part of which is below, and sets out the two parties' current negotiating stance:
UK–EU trade disputes
If the UK government concludes a comprehensive free trade agreement
(FTA) with the EU within the transition period, that agreement will
set out a way to resolve ...