This bug report is rejected as file size is not an absolute measure of lossless. The lossless H.264 preset was changed to not be intra-only (only I frames), and now has a GOP size of 25 frames. This allows creating much smaller files while still being lossless. You need to look at the resulting file with MediaInfo and ffprobe and look for the H.264 profile is “High 4:4:4 Predictive”. I just ran a test, and I see it. It also plays fine. Another thing you can do to verify is right-click the completed export job and choose Measure Video Quality, wait for that job to finish, right-click it, and view the report. You should observe 1.0 values for the ssim[Y] column
If you want intra only, change the GOP to 1. If you want a large file size (difficult with only 10 seconds as your video is “Length 00:10:02”) use Ut Video.
Here is a video quality report using Ut Video
This one shows numerically absolute lossless while x264 is so near lossless I guess it is considered close enough (like 99.99%).