Great suggestion I will try that

try to allow the tablet to play in the back ground kinda..if he stops and rewinds the video ect. Let him put keep returning to the task. Maybe see if he is ok with it being near but keep on the task?
ive had to do it and still sometimes. Maybe that will help. Just a suggestion.

The only thing I see him keeps him sitting down it’s is tablet but I don’t want to relay on the table too much , although we use the tablet when go doctors appt n travel on the car a long distance

Can maybe try really fun toys that they only get when sitting like: spinner top, light up spinning toy, favorite game, special senory ball, silly putty, shaving cream, try start with them do a simple 3 piece puzzle give reward for putting puzzle piece in like few m& ms until all the pieces are in, the do a really fun toy actvity, with the goal of sitting. Also let them up soon as they are finished.
just thoughts and how we did with the help of ot, i had a two year old that could rearrange the furniture but didnt sit for extended periods and struggled with attention as well....

Great option but his attention span is very short