Common thresholds I've seen talked about are 220 and 225. I've also heard that it's fluid and can change from day to day at any program - maybe that's why these data aren't made publicly available...
You seem to be asking multiple interrelated questions, so let's tease them out.
Q1. How do IM programs treat Step 2 scores?
A1. In the 2024 match there were 707 IM programs offering 10,261 categorical IM positions. You can therefore expect about 707 different approaches. This can range from high and very rigid thresholds to places that have no threshold and will spend time looking for diamonds in the rough.
Q2. Will a higher Step 2 score provide benefit in the match?
A2. Absolutely. While programs look for different things, the higher the score the more likely it will be that an application survives any type of raw metric screen that is applied.
Q3. Can a US MD senior with a 230-240 Step 2 score match well in IM?
A3. Absolutely. While there are super-competitive programs in IM, overall it is not a competitive specialty. If every US MD senior who applied to IM this year matched in IM, there would still be over 6,000 leftover positions. An average applicant from a mid-tier US MD school with no red flags starts out in a very favorable position relative to much of the IM applicant pool.
A3a. To head off the inevitable pushback on A3, no, just looking at the number of IM applicants to positions obviously does not tell the whole story. IM programs can range from historic, high power, heavily academic, urban tertiary referal centers with 95 fellowships, to small community programs in isolated parts of the country. However, the fact remains that US MD seniors with no Step failures or other red flags can do quite well in the match, assuming they apply sensibly.
Q4. What is the best course of action for a US MD senior applying to IM with a subpar Step 2 score?
A4. Get advice from your school's speciality advisor(s) and in-house IM PD, then apply broadly to a mixture of academic and community programs. The upper midwest has some very solid academic IM programs that are not terribly competitive because most people don't want to live there.