You are confusing what Trump is accused of doing which is inciting an insurrection and what Biden is actually doing which is abusing his power as president to have his "justice" department persecute Trump so Biden won't have to run against him in 2024.
Trump did not incite a riot, let alone an insurrection. Have you bothered to look at any of the tapes? Where can you find anyone inside the capitol being destructive in any way except the jerk who tried to steal Pelosi's podium and gavel. And EXACTLY how many guns were confiscated from the thousands who were arrested? The people who broke down the doors should be prosecuted. But when you allow BLM and Antifa to burn down police stations and occupy government buildings and not prosecute them, it is really hard for me to get behind years in prison for the people who did actual damage on Jan 6. Surely burning down a police station warrants some jail time. How about a Wendy's? Those people got community service. You do realize that for an actual insurrection, the perpetrators would almost certainly have brought guns instead of phones to take selfies. We are never going to know how many FBI agents were working the crowd inciting the riot outside the building. There is video of some of this but Ray Epps seems to be a Biden so he gets away with inciting a riot but Trump talks about marching "peacefully and patriotically" get accused of insurrection. GIVE ME A BREAK.
Regarding the Georgia case, which may be what the immunity is about. As the President of the United States, it was his duty to enforce the law. He was convinced (as are a lot of other people still) that there was corruption in the election. It was his duty to pursue that and try to determine the truth. That means, that he was doing his Presidential duty and if you decide you can prosecute a former President for something he did as part of his job, then it will never end. Every time a new party takes power, the previous administration will be persecuted for everything they did that the new administration doesn't like. There is a different between an action you don't like and one that is criminal or a violation of your oath of office. Biden is violating his oath of office with his open border policy. As the President, you don't make law. Congress makes law. The President enforces the law. He doesn't get to pick and choose which laws to enforce.
Let us not forget how Harris was contributing to the gofundme pages of actual rioters but she wasn't accused of anything.