Did you Remux the video? You have to Remux the video and then it sends it to the folder you specified.....I think.
File > Remux Recordings. A new window will open up labeled Remux Recordings. Click on the 3 little dots under the title OBS Recordings.
A new window where your recordings are saved will open up. You're looking for an .mkv file and it will be labeled with date and time.
Mine looks like this: 2023-06-28 19-25.mkv. Once you select the .mkv file you want (the last recording you did?), select Open in that window and then in the Remux Recordings window, that should now be visible, click on Remux. It'll show you when the Remuxing is done, click OK.
Now go to where your recorded files from OBS are stored (probably the same place as the .mkv files are?) and the Remuxed file will now be labeled 2023-06-28 19-25.mp4.
Someone will comment if I am wrong....