Thanks for sharing the code here. It looks like the image element is contained within a paragraph and that's probably what's causing the images to be cut short. Outlook will read the line-height of the paragraph and treat that as the height of the image.
Here's a bit of code to try in place of what you've posted, let me know if this helps to resolve the issue for you:
<p style="text-align: center;">
<strong>
<span mce-data-marked="1" style="font-family: helvetica, arial, sans-serif; color: #000000; font-size: 16px;">CONNECT WITH US</span>
</strong>
</p>
<div style="text-align: center;">
<strong><span mce-data-marked="1" style="font-family: helvetica, arial, sans-serif; color: #000000; font-size: 16px; line-height: 40px;">
<a href="https://www.facebook.com/heartlandbankandtrustcompany/" target="_blank">
<img src="https://go.hbtbank.com/rs/381-SGM-086/images/Facebook_Icon_80x80.png" alt="Facebook_Icon_80x80.png" height="40" width="40" />
</a>
<a href="https://www.instagram.com/hbtbank/" target="_blank">
<img src="https://go.hbtbank.com/rs/381-SGM-086/images/Instagram_Icon_80x80.png" alt="Instagram_Icon_80x80.png" height="40" width="40" />
</a>
<a href="https://www.linkedin.com/company/heartland-bank-and-trust-company" target="_blank">
<img src="https://go.hbtbank.com/rs/381-SGM-086/images/LinkedIn_Icon_80x80.png" alt="LinkedIn_Icon_80x80.png" height="40" width="40" />
</a>
<a href="https://www.youtube.com/@HeartlandBankAndTrustCompany" target="_blank">
<img src="https://go.hbtbank.com/rs/381-SGM-086/images/YouTube_Icon_80x80.png" alt="YouTube_Icon_80x80.png" height="40" width="40" />
</a></span>
</strong>
</div>
In the code above, I've changed the 2nd element to a <div> instead of a <p> and set the line-height of the inner <span> (which wraps your images) to 40px to match the height of the images.