Signature image not showing up properly on email to other providers.

As all the formatting is gone, it looks like the message is being received in Plain Text rather than HTML.

A quick way to verify this, is by also including some other formatting within the message aside from the image. For instance, some bold and italic text as well as some additional text colors.

If all this formatting is lost, then the message is indeed being converted to Plain Text.

Does this happen for all your messages to any provider or just with Gmail?

If any provider, then this is very likely happening on your side. The usual suspect is having an add-in installed which does something upon sending the message.

Which add-ins do you have installed?

If you have a virus scanner installed which integrates itself with Outlook, disable this integration and try again. Additionally, see: Disable Outlook virus scanner integration? - Robert 365