Minnesota Schedule M1M Box 1 incorrect:

turbo Tax had the same problem last; and not resolved for this test. I overrode the field and mailed my return.

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I have no solution to your problem yet, but as a fellow Minnesotan trying -- and failing -- to accurately enter out-of-state tax-exempt interest reported in MN KF Line 1 without the KF Line 1 values being doubled (in my case, by being ADDED in M1M line 1, and thus consequently in M1 Line 2, to my 1040 Line 2a total federal tax-exempt interest), maybe I can help identify the range of the problem, since I'm possibly sharing your problem. Here's the specifics, and a prediction:

Specifics: I have two different payers of simple MN KF Line 1-only entries. Consequently, my TurboTax-Online program's two MN KF Line 1 Out-of-State "Tax-Exempt Interest" (TEI) entries were summed accurately by M1M Line 1 to contribute their combined TEI sum to the M1M Line 1 -- but when it comes to the M1M Line 1 checking that its total KF Line 1 entries sum to ≤ 1040 Line 2a's total federal TEI (which contains both of the two MN KF Line 1 entries)? NOPE! M1M Line 1 goes haywire instead by ALSO sucking into its sum ALL of my 1040 Line 2a federal [total] TEI, thereby SUMMING the 1040 Line 2a total with my two KFs that comprise part of my 1040 Line 2a total -- which, in my case, creates a monster M1M Line 1 = to my first MN KF's Line 1 + my second MN KF's Line 1 + my entire 1040 Line 2a total, which contains both MN KFs Lines 1! I had to file my MN income forms last year (2023) on paper, hand-corrected, after MNDOR rejected the e-filed MN M1 state returns with THIS error code: 

"M1 Error Code 0630 - Schedule M1M: the sum of line 1 (and line 2) cannot be greater than: line 2a on Form 1040 or line 9b on Form 1040NR."
My M1M thus failed that test, by being > than my 1040 Line 2a by the exact value of BOTH of my two MN KF Lines 1.

so...

Prediction: If your Minnesota KF Line 1's out-of-state tax-exempt income is the ONLY source of tax-exempt interest reported on your 1040 Line 2a federal tax-exempt income, then your KF Line 1 would exactly match your 1040 Line 2a value -- but your M1M Line 1, and thus M1 Line 2, would be exactly double the value of the KF Line 1 and of the 1040 Line 2a, because the M1M Line 1 Box is SUMMING the KF and the 1040 Line 2a, instead of just CHECKING that the KF Line 1 value isn't LARGER than the 1040 Line 2a.

I was able to reproduce my error in ESTIMATED taxes where I've simplified the entries for KF Line 1, and for 1040 Line 2a. I suppose it could be user error, but if so it is a fundamentally easy error to make, somehow.

Perhaps your TurboTax agent can just "fake create" a test-case KF Line 1 item of $500 as one's whole income for the year, and then see if TT appropriately enters it as both a federal 1040 Line 2a $500 tax-exempt income AND as a MN KF Line 1 $500 item, but inappropriately merges them at M1M Line 1 into a $1000 taxable Minnesota income?

Does any of my experience also match anything you see?

It appears to be a slightly more complex bug than that: TurboTax's Minnesota (MN) M1M Line 1 since 2023 has apparently been WRONGLY SUMMING 1040 Line 2a (Total Federal Tax-Exempt Interest) WITH MN KF Line 1 (MN-Taxable Other-State Federal Tax-Exempt Interest) to give a FALSELY HIGH M1M Line 1 Minnesota income addition, instead of RIGHTLY SUMMING MN KF Line 1 WITH Other States' K-1 Box 14A (Federal Tax-Exempt Interest) to give the TRUE M1M Line 1 MN income addition, which would be an M1M Line 1 value = to the 1040 Line 2a value MINUS only MN-tax-exempt federal tax-exempt interest).

Consequently, upon TurboTax MN State M1 & M1M E-filing, the submitted M1M Line 1 total (which if calculated correctly represents everything in 1040 Line 2a's Federal Tax-Exempt Interest EXCEPT its small values for MN in-state Tax-Exempt Interest) is then automatically "error checked" by the MN Dept of Revenue to ensure that "M1M Line 1 ≤ 1040 Line 2a" -- and thus the e-filed TurboTax MN tax return is rejected, because it's rightly flagged as showing "M1M line 1 > 1040 Line 2a" for having twice-submitted (thereby doubling MN state income taxes on) any MN KF Line 1 value entered as a KF Line 1 value AND again in the 1040 Line 2a value. 

I have no resolution to correct it, but TT says they're now working on it (search M1M and KF line 1).