Certainly it was every day last summer.
I think the frequency was reduced for a while after Covid but has been daily (all year round) for some time.
Anyway it's easy enough to check (and buy tickets) on the CFR ticket. (I wouldn't bother with the Moldovan railways web site).
I'd highly recommend it - quite an experience.
But if you get it towards Chisinau and want to take a photo of the rather impressive engine I'd be prompt about getting off.
And you should also watch this: