Yes, it is laggy, and its not a hardware issue.
My specs:
i5 9600H, Gtx 1660ti (6gb), 16gb ram.
And we both know that this game doesn't require AAA specs.
I know and I have the same HW as you (the only difference is that I have a GTX 1080) and I don't have any problems or lag in relation to the UI (or any other kind), never.
You have to have the drivers updated.
Run Ccleanner or similar from time to time.
Do a virus/malware check from time to time.
And in general maintenance of the PC from time to time.
And above all run the 64bit .exe which should work better than the 32bit one.
I've tested the game on PCs with limited HW and it runs smoothly with no lag (UI) and people don't report problems/lag related to the UI (many people play with limited hardware and have never complained about the UI, including the patrons).
Ok, ive just tested the latest version, its running perfectly fine, but the previous versions were a bit laggy,
Lag means, when i click for any option ingame, be it anything in the menu or interaction with the characters, it stuttered a few milliseconds before responding.
Other than that everything was running perfectly, all the animated scenes included
These things can sometimes go through the "persistent" file which is the one that holds all the variable cache. I always delete it in each new version but sometimes it can cause strange behaviors.
Anyway, I've been testing, and thanks to an option in the code I've managed to fix the current problem in 0.6 with the map (random lag/spikes) and it seems that everything is running a little more smoothly.
The solution has been to increase the image cache and now it uses a total of 500MB of RAM approximately. I have to keep testing because these things can go very well but if you touch more than you should... it explodes.
I'm glad this version is going well for you, enjoy the bunnies.