We still know so little about the microbiome that’s it’s hard to even say with certainty that more microbes is better or worse than less. We do know that a lack of fibre leads to a lack of microbe diversity, and we also know that that diversity is quickly restored upon re-introducing fibre. Mouse models suggest that it takes several generations before a lack of fibre permanently alters microbiome diversity. It may be that we are designed to be healthy with seasonal fluctuations in microbiome diversity.
That said, if your goal is ketosis, it’s important to distinguish between total carbs and NET carbs. 20g net carbs will keep anyone in ketosis, and my recommendation is that for optimal nutrition, especially in the absence of organ meats, one should make use of that fact and subtract fibre from plant foods, which will allow a much higher amount of fibre in the diet as well as important micronutrients.