I totally understand where you’re coming from. What I’ve been trying to do is very gradually up my calories so my body gets used to being leaner. Since I stopped actively dieting down around March, I’ve only gone up by 300 calories per day.
Now, while I’m not really overly familiar with keto/auper low carbs at all, it obviously worked for you so I’d be hesitant to say change everything. What you could try would be this, and I’m going to go ahead and tag @robstein so he can pull me up on any mistakes:
Phase 1 - add around 50 grams of carbs per day on training days only, and have it all during and after training. So, something like dextrose or maltodextrin would probably work well. That’s an extra 200 calories per training day, which isn’t much. Do that for something like six weeks to two months.
Phase 2 - add an extra 50 grams of carbs per day on training days, so you’re at a total of 100 grams per training day. Spread it immediately before, during and after training - so maybe oats before and after on top of the dextrose. Do this for another six weeks to two months. You could possibly drop you fat to compensate for the extra calories from carbs if you feel the need, but I think it’ll be unnecessary
Phase 3 - start adding 100 grams of carbs to your non-training days too, either spread throughout the day or just in the morning and evening, from sources like oats, rice and potatoes. Do this for another six to eight weeks
Phase 4 - by now your body should be pretty well adjusted to using more carbs so you could start gradually adding more and more until your find your sweet spot for lean growth