The Longman Dictionary of Contemporary English defines “yes, but…” as agreement with reservations. The example sentence they give is

‘There are still a lot of problems with Jeff’s proposal.’

‘Yes, but it’s the best one we have.’

–https://www.ldoceonline.com/dictionary/yes-but

Their example sentence illustrates their definition, of course. My example sentence starts:

“Are you ready for go-live on Monday?”

“Yes, but…”

I define “yes, but…” as “no.” Continuing that conversation,

“Are you ready for go-live on Monday?”

“Yes, but it’s at risk [in this way].”

“How much risk are we talking about, and what are you doing to mitigate it? Are you actually ready for go-live?”

Can’t you see the blood pressure of the questioner climbing? The visual I have for this is a cartoon character with their whole body as a thermometer that’s about to blow its top. Re-imagining that conversation with “no” instead of “yes, but…”

“Are you ready for go-live on Monday?”

“No, but we’re close. There’s this risk, and we’re mitigating it like this. We will be ready, but we’re not quite there yet.”

“Yes, but…” means “no.” So just say “no.” The conversation can continue from there, productively.