In Jain Dharma, the ideal of muni / sadhviji conduct is complete restraint and very careful observance of ahimsa, aparigraha, and non-attachment. In that sense, using a microphone is not part of the classical ascetic ideal.

However, in practice, some communities accept it as a utility for preaching, especially where it is seen as helping more people hear the pravachan and understand dharma. Others reject it as a deviation from strict restraint. So this is a matter where different Jain traditions and acharyas may differ in acceptance.

What is important in Jain perspective is:

• The monk’s vow of restraint
• Whether the use increases worldly dependence
• Whether it is truly necessary or just convenience
• Whether the sangh is following a tradition approved by its acharyas

So your concern is understandable from a strict Jain ascetic viewpoint. At the same time, many followers accept what their guru-parampara teaches them. In Jain Dharma, people often follow the guidance of their acharyas and panth traditions.

If you want, I can explain this specifically from the Digambar or Shwetambar viewpoint.