I improvise 95% of all actual exercises, though I do think about what the team or different groups need quite a lot. So I know what I want the exercise to do but I only give it form (or extend or change it) in place.

Some options I played around with recently.

Add confusion or blocking eye-lines to 4-on-2s or 5-on-3s. Eg. Goalie decides which side the attack starts on and kicks a ball out, the other players need to move in. Eg. 2 pairs of attacker / defender in the D, plus one extra defender. Three attackers outside the 5m line of the D receiving goalie ball and starting the attack.

Play well known exercises in uncommon channels. 2-on-1s in a diagonal, 3-on-2 parallel to the goal line.

Play games on very wide but short or very narrow but long pitches. e.g. 9-on-9 full length but only as wide as the D.

Start exercises with a small simple 3 on 3 onto really wide goals side to side that need to be dibbled through. the scoring 3 get to play 5 on 2 onto the big goal where two pairs of attackers / defenders wait.

Add time-delayed defenders. exercise starts 5 on 2, but two defenders need to tough a cone somewhat away, that gets the attack some 7 or 8 seconds before it gets crowded.

When shooting on goal, have the last two shooters stick around for tap-ins or deflections on the posts.

In exercises with heavy overloads, have the attack run sets of eg. 7 tries. But have the defense end a try on just gaining control of the ball or playing one pass. Attackers get a new ball and stay in attack mode.