Where is the microphone in WhatsApp after iOS 26 update?

Go to Settings > Privacy & Security > Microphone, and make sure WhatsApp has permission for the Microphone. It is the app that asks for permission and app updates can change the status and it has in the past too. The prompt to grant permission is also initiated by the app and the app will not have access to the Microphone until it gives you that prompt and you accept.

It really does not matter who you want to blame, it is a third party app provided by Meta to work correctly on your iPhone. If any app is not working correctly, it is the developers responsibility to provide support to their users and resolve a problem. Apple, or even Android for that matter, is not designing their OS to support WhatsApp, it is Meta that designs the app to support the OS.

https://faq.whatsapp.com/

Allan Jones wrote:

In the last few months Meta has released several updates to fix their bugs, including security issues. Suggest you update WhatsApp to the current version if you have not already

Correct, and for WhatsApp specifically, there have been 12 updates in just the last month with the most recent one being 3 days ago. Some of those did introduce bugs that required a follow up update to resolve. That is a pretty good sign that very little in-house testing is being performed and the users are actually the bug testers. On average that is a little more than 1 update every 3 days, and Meta has no community forum such as this where users can discuss the issues they have found.

What are the other applications?

WhatsApp is not an Apple product. It is owned by Meta, along with FaceBook. Unless the "other apps" are Apple apps, you need to start with WhatsApp support:

https://faq.whatsapp.com/

In the last few months Meta has released several updates to fix their bugs, including security issues. Suggest you update WhatsApp to the current version if you have not already