Company: NMZ
Filing Date: 2025-07-07
Form Type: N-CSRS
Source: 0001193125-25-156000
Chunk: 75

Company: NUVEEN MUNICIPAL HIGH INCOME OPPORTUNITY FUND
Filing Date: 2025-07-07
Form: N-CSRS
Chunk 75
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 the period covered by this report that has materially affected, or is reasonably likely to 
 materially affect, the registrant’s internal control over financial reporting.                                                                                                                                                                                            |

| Item 17. | Disclosure of Securities Lending Activities for Closed-End 
 Management Investment Companies.                           |

Not applicable.

| Item 18. | Recovery of Erroneously Awarded Compensation. |

| (a) | Not applicable. |

| (b) | Not applicable. |

| Item 19. | Exhibits. |

| (a)(1) | Not applicable to this filing. |

| (a)(2) | Not applicable to this filing. |

| (a)(3) | Certifications pursuant to Rule 30a-2(a) under                                                            
 the Investment Company Act of 1940 and Section 302 of the Sarbanes-Oxley Act of 2002 are attached hereto. |

| (a)(4) | Not applicable. |

| (a)(5) | Not applicable. |

| (b) | Certification pursuant to Rule 30a-2(b) under                                                            
 the Investment Company Act of 1940 and Section 906 of the Sarbanes-Oxley Act of 2002 is attached hereto. |

SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized. Nuveen Municipal High Income Opportunity Fund

| Date: July 7, 2025 |     | By: |     | /s/ David J. Lamb            |
|:-------------------|:----|:----|:----|:-----------------------------|
|                    |     |     |     | David J. Lamb                |
|                    |     |     |     | Chief Administrative Officer |

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

| Date: July 7, 2025 |     | By: |     | /s/ David J. Lamb             |
|:-------------------|:----|:----|:----|:------------------------------|
|                    |     |     |     | David J. Lamb                 |
|                    |     |     |     | Chief