If I get mythic I'll make a complete sideboard guide.

Initial Remarks

I made the initial version of this deckon MTGArena on 18th of April, 2 days after Ikoria release. Been working on it ever since, with current win rate of 68% on Diamond 3.
I had a few iteration of this deck on the past few days but I feel I'm getting to a good point on it.
I was very inspired by the Jeskai Control from the Dominaria Era, with Teferi, a lot of controlling card, card advantage and HUGE threats. I loved that deck and I think it was the first deck that I had completed on Arena.

Ikoria has brought some new friends to the Jeskai Decklist: Shark Typhoon, Narset of the Ancient Way and Raugrin Triome. There are some other additions but they feel weak to me, and I'll talk about them.

Narset of the Ancient Way delivers a lot of good thinks to a control deck: life gain, card advantage, board control and a win condition. Her +1 is clearly the weakest of her kit, but the additional mana can be used to play a Shark Typhoon turn five or help you complete your mana to cast impactful spells on the same turn. Her +1 also gives you life, which can help you get back on the game after stabilizing against an aggro opponent.

Raugrin Triome is pretty self explanatory: it fixes your mana early on and also can give you card advantage or give the additional +1 attack to Dream Trawler on the right moment. A great card.

So Shark Typhoon... I laughed at this card on release because it's a clear reference to a very bad movie but man... I regret laughing. A lot.
I've won so many games because of this card it's insane... The cycling cannot be countered and the ability is just insane value for a Deck with a lot of cards that can be used on the opponent's turn or have a high casting cost. This is also a card that can anwser a Teferi, Time Raveler after he hits at turn 3, because cycling is not considered a spell therefore, Teferi's static ability doesn't apply to it. It's bonkers, there's nothing more to say about it. I think it'll be an addition to most of the U decks of the meta. I'm trying this card on Temur Reclamation and Band Midramp too.

There's also some new cards added from Ikoria like Inspired Ultimatum and Yidaro, Wandering Monster but those cards are not so good. There some decks that are runing them but I prefer my version.

Yidaro, Wandering Monster, for me, is a meme. It takes a lot to cast it, unless you get ultra lucky and have an insane draw and get all four one after another. A control deck has to be consistent, and this card looks like the opposite of consistent. For me this a dead card. If you're looking for a cute jank card it might suit you, but I don't like it.

And now Inspired Ultimatum... I liked this card at first and I think a lot of people did too. But after playing it, I think it's trash. 7 mana draw 5, gain 5, deal 5 that can take Aether Gust or countered on turn 7 by Mystical Dispute is just bad. It's heavier than Dream Trawler which is a card that destroys games but it doesn't do too much.
A lot of people compared it to Sphinx's Revelation but this at best a worse version of that card. It's not a mana sink and it's a SORCERY, and that makes a HUGE DIFERENCE. Dealing 5 most of the time is irrelevant and tapping out on YOUR turn to gain 5 life, draw 5 and probably have to discard some cards is honestly bad I'm sorry.

After this brief explanation on why I like the deck, I made a initial sideboard guide for the deck. As I said previously I'm still working on the deck as it's only about 3 day old, but I'm getting good results with this sideboard strategy.

Just a reminder that sideboard plans are not the absolute truth and you must always adapt to your opponent's deck. This is just the way I'm playing on the moment but the meta is always changing and your sideboard plan should change too.

Sideboard Strategy

vs Flash Dimir/Simic
-2 Aether Gust -1 Chemister's Insight
+3 Mystical Dispute

This match is not that difficult, fight for tempo against the flash deck and try to land a Teferi, Time Raveler. Be careful on game 2 for possible side counters, try to play around it. Abuse Shark Typhoon in this match: as cycling is not a spell, it can't be countered and opponent likely removed his/her removal spell on to the side, so this card can get your opponent by surprise.

vs Gyruda Bant
-1 Narset of the Ancient Way -2 Chemister's Insight -3 Deafening Clarion
+3 Mystical Dispute +2 Grafdigger's Cage +1 Shatter the Sky

In my opinion, this deck is favored against Gyruda, Doom of Depths. Hold your counters for Gyruda, Doom of Depths and try to kill the mana dorks opponent plays. Game 2 gets a little trick with the addition of their side, with possible counters and specially with Destiny Spinner. Destiny Spinner can easily screw our game by making Gyruda uncounterable, and landing a Gyruda might be very bad for us because we run Dream Trawler

vs Mono Red
-2 Dovin's Veto -2 Chemister's Insight -2 Shark Typhoon
+2 Archon of Sun's Grace +3 Devout Decree +1 Shatter the Sky

Aggro is always a hard match for control decks, but this side plan is pretty straight forward: trade some card advantage and late game threats for board control and damage mitigation/life gain. I'm still figuring out if keeping Shark Typhoon in this match is worth it because of the cycling ability, but one of the 2 late threats has to go.

vs General Control
-3 Deafening Clarion -1 Narset of the Ancient Way
+3 Mystical Dispute +2 Narset, Parter of Veils

I know theres one missing card on the side out but this is the general idea. Depending of what type of control you're against, you'll side differently. Maybe you're against a non red/green control then side out Aether Gust. There's a few options on side vs multiple controls. A card that's been surprisingly helpful vs control is the Scorching Dragonfire for a few reasons:
1 - It can hit the Narset, Parter of Veils on turn 3 after your opponent just casted her or Teferi, Time Raveler on your main phase.
2 - There are some types of control-like decks that run some early game aggro card on the side, like Robber of the Rich or Spectral Sailor.

vs Jeskai(or others) Fires

I'm using the same sideboard strategy as vs General Control, although the deck is considered to be more of the midrange type. This is a match that Aether Gust shines and it's why I didn't include in the side-out of the vs General Control Section. I think this card has proven itself enough on the previous sets and it continues to be strong as Red Decks are always in the metagame. Being able to delay Cavalier of Flame, Fires of Invention or the newly added to the Fires decklist Keruga, the Macrosage is huge. Not only delaying the arrival of those cards but also not giving your opponent a possible impactful new draw.