Though a patch was teased earlier this year, it seems like development is nearing completion. As reported by PlayStation Game Size, a 6GB update is supposedly being tested internally.
New Returnal Update Is Being Developed, Possibly Adding Mid-Save Feature
The patch's significant size hints at the addition of new content and features, one of which could be an oft-requested mid-run save feature. Though Returnal was applauded for its challenging gameplay, the lack of mid-run saves was criticised, since playthroughs can take significant time to complete.
In a previous interview with Axios, Housemarque stated that a mid-save feature was being considered. On the other hand, this file size could also hint at the addition of more missions and quests.
The patch hasn't been announced officially, but given the fact that it has supposedly entered beta-testing phase, a reveal could be unveiled soon. We'll inform you when these details are publicly confirmed.