OpenShot Video Editor is a video editing software that lets you create images with text or additional pictures to overlay on videos. These images have transparent backgrounds and are called Titles. OpenShot provides several templates with its Basic title editor. You can select a template and fill in the fields such as File Name, text to display, Text Color, and Background Color. You can also change your title's font, style, and size using the Change Font button in the Basic editor.
If you want more control over your title overlay, you can use Inkscape, an image editing program, as the Advanced editor. Install Inkscape and configure OpenShot to use it. In Inkscape, you can use the fonts installed on your system to create your title overlay. To ensure the font appears in OpenShot, you may use paths to convert the text to an object. Once you have completed your title overlay, save it and import it to OpenShot as a title. Here is a link to a video tutorial demonstrating how to use the basic and advanced editors in OpenShot. https://youtu.be/nNSf7CMFFWY?t=440
You can also create an image with a transparent background and text using any image manipulation program such as GIMP, Photoshop, or Inkscape. Import this image into OpenShot and add it to your timeline on a track higher than your video.