A video channel can have multiple niches if it's based around a person or personal brand. For example, family vlogging channels often feature multiple people with different interests. Vlogging is a great way to build a personal brand and loyal community around your channel.
Here are some tips for having multiple niches on a YouTube channel:
Build your personal brand
Focus your brand around yourself so you can authentically talk about different topics.
Create videos about multiple topics
If your channel is based around you, you can try to create videos about multiple topics.
Combine niches
You can combine niches to stand out. For example, you can create fitness, lifestyle, and health videos.
If your channel isn't based around you or your life, it's best to stick to a single topic or niche. This will help you avoid having a segmented audience.