Yeah. A Chinese court can probably easily differentiate between "recognising" a factual instance of bigamy (or in this case, lesbian cohabitation) while still treating it as an illegal act, and "decriminalising"/"legalising" a practice by court judgment. I would assume that any legal system would inherently need to be able to do the former without necessarily overreaching into the latter, because if that ability isn't there then it may be theoretically possible to perversely argue that judges actually cannot impose derivative criminal libilities or pass sentences on convicted persons because courts should not recognise (i.e., legalise) a crime by doing so. In general, arguments along the pattern that a civil case cannot be won because a requirement of the relevant civil law concept is already criminal act are inherently silly, since nobody is going to argue that a civil case to get compensation for physical battery cannot be found because battery is also a criminal offence. It's the literal/plain meaning rule being taken to the dumbest conclusion, i.e., the cases you teach in law school (if such cases exist) to show why concepts like the mischief rule/golden rule/purposive approach are necessary.

In fact, the current situation is probably a weaker case than the bigamy example that you provided, given that unlike bigamy, "cohabitation" (or infidelity) is not even a criminal act per se, just a criteria to tick so as to fulfil other legal liabilities. So, the court can easily just say "we recognise that people sometimes have gay/lesbian relationships outside marriage, and that for LGBTQ people such relationships fit under the definition of "living as if husband and wife" without seriously worrying that somehow according to some crazy literalist interpretation they've created gay marriage. Somehow I don't think LGBTQ activists in China would view that as commendable and actual progress towards legalisation of gay marriage.