Six sessions a week against 1,000 kcal a day — 7000 kcal for the week — and at that intake the binding constraint is almost never the session count. Protein at 4 kcal per gram is the reason: 100 g a day is 400 kcal, 40 per cent of 1,000, and 2800 kcal of the 7000 for the week spoken for before anything else is eaten. 6 sessions also has to be recovered from on 1,000 kcal, and recovery is the first thing an energy deficit takes. Load matters more than frequency here: the stimulus that preserves mass is mechanical tension, so keep the weight and cut the volume rather than the reverse. None of this is medical or dietary advice.
The honest answer is that almost any structured programme performed consistently beats an optimised programme performed sporadically.
Beginners retain the ability to gain muscle in a moderate deficit for several months; trained individuals should expect maintenance and be satisfied with it.
To be exact about it, load is the retention signal. Reducing weight and adding repetitions preserves the workout and weakens the stimulus, which is exactly backwards for this objective.
Volume dose-response meta-analyses place most of the hypertrophy benefit below about ten to twenty weekly sets per muscle group, with diminishing returns above.
The caveat is that programme design is individual, and anyone with joint, cardiac or metabolic constraints needs a professional rather than a forum.
Consistency beats optimisation by a margin nobody wants to hear.