Outlook make your emails look distorted or increased in size for some users while other users might see images reduced in size.
Display size in Windows is not 100% but set to either 125% or 150%.
This causes the signature to increase/decrease in size.
Simply reset your display size to 100%.
This issue affects Outlook (desktop)
If you know HTML, you can start HTML coding your email signatures to accommodate for users with desktop scaling.
The challenge for email signature designers is that Outlook doesn't read the HEAD section of the HTML when the email signature is pulled into Outlook > Learn more.
How to set Display text size to 100% (default)
Reducing the resolution from 3200x1800 down to 1600x900 will still look reasonable since it's pixel doubling, then you can set DPI scaling back to 100%.
Open the DPI scaling on a windows machine by navigating to your display settings > Make text and other items larger or smaller:
Here you select 100% (default):