OBS Studio 21.1

Open Broadcaster Software Studio is an open source software program designed for individuals who seek to create and share multimedia content over the Internet through social media services such as YouTube, Twitch, DailyMotion or Facebook.

Software installation goes smoothly the most difficult being to wait for the program to be downloaded.
The interface, though it may be minimalistic for some, it lacks nothing. I didn't encounter any issues regarding theme color or the contrast, and the buttons are very visible, though the text size of some themes could've been one or two pixels bigger.
Also, the fact that it has a theme selection option it's a plus.

The program functionalities are various and numerous.
First, the studio mode lets you preview scenes and sources before making them public. You can choose from a number of different and customizable effects between scenes or add your own stinger video files.

Next, with Modular 'Dock' UI you can rearrange the layout as you wish or pop out each individual Dock to its own window.
The multimedia capturing offers high-performance mixing possibilities with options like the content creation from multiple sources or an unlimited number of scenes switch between custom transitions.

Also, OBS supports all your favorite streaming platforms and, if you're a beginner, it has tutorials that cover all the important aspects that you want to know.

All in all, those who developed this software and who are improving it continuously, for free, are to be appreciated for creating a very useful streaming tool.