Help with Steam Library on Ubuntu

I'm looking for an expert to help me with my Steam app on Ubuntu. My hard drive is formatted as EXT4 and I'm new to Linux. I have manually mounted the drive, but I'm unable to add it as a Steam library location.

Ideal Skills:
- Deep knowledge of Ubuntu and Steam
- Experience with EXT4 file systems
- Strong troubleshooting skills
- Ability to explain technical concepts in simple terms