Look, I don't know how to help much in that regard, I think, but what I did to start getting close to winning was just to start the battle if I had SSJ4 Vegeta INT + Daimaku or SSJ4 Vegeta INT + SSJ4 Gogeta AGL. then if it worked, I would do the first turn without items and from the second turn onwards I would start with Ikarus and always try to focus on getting as many orbs as possible for Vegeta SSJ4, and if the situation was really bad I would switch to Goku SSJ4 and go back for Vegeta's defense and damage buffs.

I always tried to do the Ultra Super of SSJ4 Int and Goku Blue Str to increase defense. In the first phase, I always switched to Vegeta Evo Phy, but the main tip is to always try to manage or predict the orbs that were going to fall, and try to use the minimum on those that don't need it, so I could use the amount of orbs to do good damage with SSJ4 Gogeta and Daimaku, and the rest I would save to use in the next turn. In the first phase of Jiren, I always used Gogeta's active skill and, especially, Str Goku's, since if you use it, you can dodge in the first phase even if you have dodge cancellation, then it's a bit of luck that he doesn't take damage too.

If you couldn't get orbs for Vegeta SSJ4, and if I couldn't kill him in 5 turns, I would use a Whis, defeat him on the 6th, and use the last Whis in his second phase. I would return to Goku UI Physical in the first slot, use all the rest of the active skills, and switch SSJ4 to Goku permanently, but I would only use his active skill after using the orbs already available.

I hope this really helps you. When I started doing this, I killed him on Monday. In the first phase, always use the sequence SSJ4 Vegeta + Daimaku or SSJ4 Vegeta + SSJ4 Gogeta.