May I know:
1- What is the max Conference Call user for Internal 3CX User in V18?
1- What is the max Conference Call user in 3CX to conduct Conf Call meeting?
For a voice call it's the simultaneous call limit of your license. Each person on a conference call is 1 SC (they each call in to the bridge).
For a video conference it's 25/100/250 per https://www.3cx.com/ordering/pricing/.
To clarify what @SteveITS mentioned, bear in mind that within a video conference calls, the max number of:
Audio Streams is 50
Video Streams is 16
This means that if you have a Ent License key, you can have up to 50 participants sending/receiving Audio, out of which 16 can also be sending Video from their Webcam, and the remaining 200 participants can receive the Audio and Video the other participants are transmitting.
The limits remain the same as per the pricing page posted above.