I have a 15 year old house that recently has had a clogging problem in the waste line inside the house that leads to the outside sewer. I have seven toilets in the house. One toilet is in the basement. The toilet in the basement meets the main line in the house under the cement floor about 30 feet before it exits from the house. There is a run of about 40 feet from the north side of the house to the south side where the junction of the basement toilet meets the main waste line of the house. From this point to almost the point where it exits the house we get the line clogged every couple of weeks. I have to use a hand auger to unclog the line. There are no cracks on the cement floor to indicate settling of shifting. We have changed two toilets to gravity toilets and changed one toilet (in top floor) to a power flush toilet. This has helped but I still check the floor trap to make sure there is no blockage on a weekly basis. And at least less frequently, I will use the auger now and then. We had a camera inspect the line from the basement toilet feed to the outside and no problems were found.
I did have a plumber and asked abount the vent stacks being plugged bet he said the toilets flush well so there should not be a problem with the vent stacks.

A "hand auger" is basically useless on a main line clog, but until you use a camera and see WHY it is getting stopped up, there is no way to tell you how to prevent it.

A camera was run into the waste line ... but found no problems.

It is possible that you have a main drain that does not have the required 1/4" per foot grade. Have you tried flushing 3 toilets at the same time with the cap off to view down into the main drain just outside the house? That might make a difference with the venting if it is undersized and would rule the venting out or in...

Have you seen the video? Do you have a copy of it? Did he run it all the way to the street? Are you on city sewer or septic?