so, i must rollback to older version and copy the DLL and i can replace it in the newer obs?Try replacing the .dll from previous working version. See https://obsproject.com/forum/threads/mfx_err_unsupported-qsv-failed-to-load.163141/#post-634493
copy to where exactly?You can download 29 .zip from https://github.com/obsproject/obs-studio/releases/tag/29.1.3 , extract/copy the file and just keep your 30.0.2 install.
If that doesn't work, try the last 28 version from https://github.com/obsproject/obs-studio/releases/tag/28.1.2 or last 27 version from https://github.com/obsproject/obs-studio/releases/tag/27.2.4