There won't be a presidential election in 2026, unless the constitution is abandoned or amended before then.
I think your assessment of the effect of what the FBI has announced is spot on. That said, the FBI makes up its own mind about how to conduct its affairs. I think it is totally indifferent to being viewed as guilty and untrustworthy, and might even prefer to have that reputation - as long as it is FEARED.
The press already labels Trump as a racist, and the FBI treated his campaign as a threat to the established order and tried to undo the results of the election. I presume the FBI remains on that mission, substitution of Wray for Comey and firing of a few known bad eggs notwithstanding.
I presume the FBI continues to view Trump and his supporters as a threat, and this report is simply one of many tools useful to distrct Trump and divide his followers. it also serves to energize and encourage anti-Trump forces to "stick to the approved narrative."