Eat maintenance tdee for your goal weight to maintain your weight range, taking into consideration natural weight fluctuations.
Not doing IF won’t affect your weight gain, only eating at a constant calorie surplus will.
Ending IF may have an immediate upward impact on your weight but it will level out after a few days if you’re eating true maintenance calories (finding actually maintenance calories is another story)
These immediate large fluctuations often occur due to water retention and digestive changes.
I chose to keep doing IF (less intensely) at maintenance last time I reached goal to keep me on track. When I stopped I failed miserably at keeping to maintenance which is why I’m back here