How can I know if she is interested or not?

So I (M) have been talking to this woman for the last few months, initially only for work-related things. She is helping me set up my finances (she works for a bank).

At first, it was only about work, but later she started sharing more about herself. She also knows that I already have a partner.

How would you usually test the waters to see if she is actually interested or just trying to help me beyond what is needed?

Also, I have noticed that over the last few weeks, she has been talking more casually.

Any thoughts on how I can tell if she is interested or not, given that she knows I have a partner?

The typical IoI are there like taking about her family without asking but not explicitly since it's more kind of a work only situation.

Also i always wondered if i should hide the fact that I am taken, i have heard about the pre selection but can anyone share if it actually works in real life, where women don't care that you are unavailable for a exclusive relationship but still want you because of pre selection.

Any thoughts on these points would be super helpful