I ran into this initially when playing regularly, but I've tested with all addons disabled aside from CraftSim. The following info on testing etc is from my tests without other addons.

1. When opening the Top Gear panel it creates a significant amount of lag. Clicking to another known recipe takes 4 seconds, for example. The entire game freezes for that time, not just the addon.

2. When doing a recipe scan with "Optimize Profession Tools" checked it significantly increases the time. Running the scan without it checked (Blacksmith with 52 items) takes 1.76 seconds. Running it with it takes 2 and a half minutes. During this time the game also lags out, giving me about 1 frame every 4 seconds. I'm not moving during this time, but I can see the blacksmithing table and effects lagging out hard.

The addon seems to run smoothly as long as I don't have any options selected involving profession gear use. It happens on almost all professions, but it does not happen with Cooking, Fishing, Herbalism, or Mining. The latter three I didn't test with the recipe scan for obvious reasons. Just by swapping between journal listings while I had Top Gear selected.

This has happened since TWW launch, but I gave it some time in case it sorted itself out. I didn't check how it worked without addons until today, and I didn't see anyone else mentioning this issue in Discord or on GitHub so I figured I'd let you know. I'm assuming it's just a me thing somehow since it's not being talked about, but I'm not quite sure what else to adjust to help. I'm not seeing any error messages when I launch with only CraftSim (aside from the one letting me know there are no datasources, which makes sense when it's the only addon going.)

I'm not quite sure I'm understanding what you mean by asking if all items from my blacksmith are the same, so if I'm answering this wrong I apologize! I checked and almost all generate lag when switching to them yes, if that's what you mean! The ones that don't are the ones where stats don't matter (Recraft, Everburning Ignition.) I did notice that the Coreforged Repair Hammer is quicker to resolve, but still has a little lag when switching to it. That one only factors in Resourcefulness, Crafting Speed, and Multicraft which I assume is the reason.

In addition I tested putting all profession gear aside from the ones I was "wearing" into the bank. This did cut down on the lag my a fraction of a second. Unfortunately not having those tools are part of the process defeats the purpose of using it. When doing this, I did realize I had a bunch of extra tools in my bags that I didn't need, so that was likely slowing it down more, but the lag is still very present even with the fewer tools.

I timed the recipe scan again while only having the equipped tools and two extra hammers in my bags. That brought the time down to 42 seconds which is usable. With the minimal tools in the bag it's definitely noticeably better, but still slower than what I ran into in DF. Overall it's not a dealbreaker, but definitely a noticeable difference.

hm yeah I guess its because of the high amount of possible combinations
are all items from your blacksmith the same?