I attended a talk last week about Type 1a supernovae with the focus being on double-degenerate systems as potential progenitors for them. We were shown a graph of White Dwarf (WD) mass distribution like the one below (source), and it got me thinking, because even though they are very faint objects they are also very numerous in our galaxy. So this led me to wonder what is the furthest known WD from Earth given that they are so faint but so numerous. I have looked for an answer online but the closest I got was a Type 1a progenitor at redshift 2 called "SN UDS10Wil" but this is not what I am looking for because this is not observable from Earth, it is just inferred from the supernova classification.
There is the unusual white dwarf RX J0439.8−6809. It seems to be a carbon-oxygen white dwarf with a temperature of around 250,000 K! It is 9200 pc away. You might want to look for other PG 1159 stars to see how far they can be detected.
Based on a Simbad search, it looks like the most distant white dwarf is WD J0106-0014, which was measured in Debes et al. 2011 to be at 6442 pc. Here's the Simbad page: