I have router mikrotik rb2011uias-2hnd OS version 6.46.1

I'm asked by my manager
1 - how many clients can connect to WiFi simultaneously
2 - how many clients can connect to Ethernet simultaneously

please guide me how I can give him a correct answer

The answer is easy ... as many as you wish if only they do not use functions which are limited by license:
Read this: https://wiki.mikrotik.com/wiki/Manual:License

The question is ... does this router is powerfull enough to serve all connected clients?

Hey. If your clients are common fttb clients then I believe 24*4=96 with 100 mb/s tariffs max. 4 Gigs for switches and 1G uplink. And queues configured off course. And you can use 100M or 1G from thos 4 for WiFi AP.

I have router mikrotik rb2011uias-2hnd OS version 6.46.1

I'm asked by my manager
1 - how many clients can connect to WiFi simultaneously
2 - how many clients can connect to Ethernet simultaneously

please guide me how I can give him a correct answer

If you want a proper IT approach to these generic questions the following will guide you effectively

For wireless the key question is how many wireless clients will be able to use our current wireless system in view of the kind of work they are expected to perform efficiently?
For wired the key question is -- is our Ethernet backbone capable of handling the kind of work our wired/wireless clients are expected to perform efficiently?

This means that you have to understand the LOAD placed on your mikrotik rb2011uias-2hnd by all the clients --- that means you will need to take some measurements over a period of time for each transport [wired/wireless] -- -- now once you have that you can provide your boss with a proper answer that will elevate you in their eyes.

Something to think about -- when the load is heavy fewer clients will be able to work effectively -- when the load is light far more clients will be able to work effectively.

What is LOAD? Streaming Video, VoIP, Video Conferencing, Cloud Data access and storage, graphic intensive work like centralized CAD, moving large files around between peers, collaboration places a heavier load on the backbone; email, browsing the internet places a much lighter load on the backbone

Simply ... you ask a question:

Will my planned restaurant 100 sqm size be big enough to serve all clients?

No info of of place where this restaurant is planned? What food do you want to sell? When it will be open? How many tables do you plan? How many chairs or benches do you plan? Will you offer takeout dishes? How many peple do you want to hire? ... and so on ...

Why did he ask this question? And why did he ask you?

Why did he ask this question? And why did he ask you?

I don't dare to ask him
I'm IT manager ( you can say I'm the whole IT Department )