First, I have no idea how it‘s done online. I simply don’t play.
However, there are issues otb:
How to castle properly? You are not allowed to use both hands.
There are positions where your King doesn’t have to move. What if you touch your King? Actually, there are positions where the King just moves one square. Has he done so the opponent „has the move“ (in principle he could move before the opponent completes castling), according to the rules. How distinguish between K/R move or castling.
One idea: one could change the rule that one always has to start with the „illegal“ part of the castling double-move.
Important reminder: your opponent has the move when you execute a legal move. Not after you have pressed the clock!
E.g. this perfectly legal:
Player A moves a
Player B moves b
Player A presses the clock completing a
Player B presses the clock completing b
lololol...you cannot be serious!!
According to FIDE, the recommended method is to set the king just off the board, behind the intended castling square, then move the rook, then place the king.
#4, that’s probably a good approach not to interfere with the issues mentioned. Not bad.
The king is always besides the rook so it is done in Chess960
White moves Kg1 (in order to castle), Black has the move and checkmates in Blitz speed.
You have to castle the other side.
#7 best way to castle in online is to move king over the rook. It will work. In that exampel there are no castling flags so you cannot castle at all
FEN needs to be 4qk1r/6pp/8/8/8/8/6PP/4QK1R w K -
You cannot castle if your king or rook has moved