Graph 8 shows the net new debt issuance by the governments of the US, the euro area and Japan, and the net purchases of sovereign debt by their respective central banks. It shows that the peak net purchases by the official sector occurred in 2016.
This happens to coincide with the low point in sovereign bond yields, but I would not attribute full causation to that. The central bank purchases are a reaction to the macroeconomic conjuncture at the time which itself has a direct influence on the yield structure. That said, one of the main aims of the central bank asset purchases was to reduce the term premium.