It is always nice to see lower scale weight (if that is what you are looking for).
But, it is likely mostly water weight - with (due to IF and good keto) up to a pound of fat depending on your overall size and how much you have to lose.
I am not trying to downplay - I am just throwing my usual warning out there - a getaway weekend, a party, an extravagant meal with friends etc. might bring some (or all) of this water weight back. The point is, down’t get down about it - just know that gain is as natural as this seemingly large jump down.
Daily scale fluctuations, especially around dramatic dietary changes can drive you crazy (because your body will hold on to different amounts of water under different schemes). In fact, given this drop - you may want to look into whether you should be having some salt in the morning - better to be “not tired” at lunchtime than to have coffee at noon (as you get older - it seems caffeine absorption slows and the 6-hour half-life turns into 10 or 12, leaving too much in your system at bedtime).
Best to measure the same day each week under similar conditions (same diet the whole week and first thing in the morning after the bathroom and before any liquids for example).