You can simply make a video of you talking through your slide deck. A view of yourself in the video is optional.
Many free tools are available to record your screen, webcam, and voiceover, such as:
Google Slides does not provide the option to narrate a slideshow and you will need to use an external tool, such as Zoom.
Screen and audio recording in Zoom: Start a meeting > Check audio settings > Share screen > Record > Save as MP4 file
If your video is in the wrong format or too large you can encode/re-encode your video with the open source software handbrake.fr.
Open your video in Handbrake > Video > Adjust the quality control toward the right to increase quality, or toward the left to lower it.