Hi Denis,

I am afraid that Helix3 does not support SVG nor WEBP as logo.

But you can try to cheat the system, and rename extension name (logo.svg > logo.png ) and choose it in Logo field (Helix settings). Of course, First upload .svg image in Joomla Media or use FTP tool.

I started testing further. And for some reason, SVG images are not displayed at all (the image width is specified in the settings). What could be the reasons?

Becuase SVG files are not PNG files, and they need defined size (width & height). Read more about that.