The investigation was about two things; Trump's collusion with Russia AND the obstruction of justice.
The report finds no overt collusion between Trump and the Russians. It details promises of influence to the Ukranians and the Russians by sleazy power brokers like Paul Manafort and Felix Sater, and Trump's associates soliciting Russians and pretty much anyone for Hilary's deleted emails but again, no substantial evidence of direct collusion.
Whether there was obstruction of justice seems like a much more legitimate cause for outrage. https://www.lawfareblog.com/obstruction-justice-mueller-repo... details the numerous ways this was attempted, though full-disclosure Brookings is left-leaning centrist think tank.
The full report is here https://www.justice.gov/storage/report.pdf which you don't need to pass the bar to comprehend, though you do need a lot of free time. I've only read a few parts but it's further confirmed my belief that all politicians (right and left) are completely unscrupulous and must be in order win. "Democracy" is a vague, fungible concept that anyone vying for power will either disregard or interpret in their favor.