Hi everyone,
I noticed that, unfortunately, in my first version, the larger I tried to make the logo, the more pixelated it became.
So I decided to place the logo directly in the Assets folder and include it in the CSS code.
The logo is now large and clearly visible.

Unfortunately, I haven't yet been able to get the same thing to work for the mobile view (smartphone and tablets). I haven't figured out yet how to target the navigation bar on the left side in CSS—where the logo should go.
I used the following CSS code, for those who are curious. It might not be the cleanest, but it works.
`/* 1. Flarums winziges Standard-Logo im Header unsichtbar machen */
.Header-logo {
display: none !important;
}
/* 2. Den Logo-Link-Container vergrößern und das echte, scharfe Logo als Hintergrund einbinden /
#home-link {
display: inline-block !important;
width: 220px !important; / Passt die Breite für dein Logo an /
height: 140px !important; / Die gewünschte Sicht-Höhe im Header */
background-image: url('https://XXX/assets/Forum_Logo_Neu.png') !important;
background-repeat: no-repeat !important;
background-position: left center !important;
background-size: contain !important;
vertical-align: middle !important;
}
/* 3. Den Header-Bereich in der Höhe anpassen, damit nichts abgeschnitten wird */
.navbar-fixed-top,
.App-header,
.Header-navigation,
.Header-title {
height: 75px !important;
display: flex !important;
align-items: center !important;
}`
I deliberately removed the forum URL from the CSS code for you, since I didn't want to accidentally promote my forum, and I'm not even sure if it's allowed to promote your own forum here.