By default, you can see up to 25 people at a time in the gallery view of a Zoom meeting. If there are more attendees than that, then you'll see right/left arrows to scroll through the screens of participants.
Zoom also has an advanced feature where you may be able to see up to 49 people at a time. Since live video meetings require significant computer resources, this is only possible if your computer meets their specific requirements.
To see if this feature is available on your computer, click your profile picture in the Zoom app and select "Settings". Then click "Video" on the left and look in the "Meetings" section. If the "Display up to 49" feature is available, you'll be able to turn on the checkbox.
If your computer is not able to handle this feature, then you will not be able to turn it on.