Which invoice style are you using? I’ve had a dig into the HTML for mine and the logo is in the DOM as
<img id="imginvoiceLogo" src="https://qfstore.blob.core.windows.net/user/.../something.png"
class="invoice-logo-img" style="width: 200px;">
so in the invoice style gallery → “customise this style” I can override that with
#imginvoiceLogo {
width: 300px !important;
}
(the !important is required in order to make the CSS take precedence over the style="..." in the HTML - normally style always wins).
There’s basically no limit to the amount of customisation you can apply to the invoice layout, but some things require much more advanced CSS than others. For example I helped someone completely rearrange their invoice sections using CSS grid layout.