Most practising Jains do not eat mushrooms.

Very simple reason: ahimsā (non‑violence).

• Mushrooms are fungi, not regular vegetables.
• They usually grow in damp / decaying places and carry many tiny living organisms which cannot be cleaned properly.
• Jain achar (conduct) teaches us to avoid foods that involve killing or disturbing many small lives; mushrooms are generally counted in that group (like root vegetables, fermented foods, etc.).

So in both Śvetāmbara and Digambara traditions, the common and safer practice is to avoid mushrooms entirely, especially for anyone who wants to follow a strict Jain diet.

You can read more here