Based on the community reply, it does not sound like typical lens fungus; it looks more like internal dust.

Fungus usually appears as web-like, feathery, or branching patterns on or between lens elements. Dust is much more common in older lenses and usually shows up as small scattered particles or a general hazy bit of debris inside. A little internal dust is normal and often has little to no visible effect on photos.

If you’re unsure, inspect the lens with a bright flashlight from different angles. If you see branching or thread-like growth, that’s more suspicious for fungus. Otherwise, dust is the more likely explanation here.

To be safe, store lenses in a dry, ventilated place and avoid damp conditions. That helps reduce fungus risk in general.