Eg, report by the bipartisan Senate Intelligence Committee (chair was Republican):
Report of the Select Committee on Intelligence United States Senate on Russian Active Measures Campaigns and Interference in the 2016 U.S. Election
Vol 1: Russian Efforts Against Election Infrastructure
www.intelligence.senate.gov/sites/default/files/documents/Report_Volume1.pdf
[p3]
II. (U) Findings
1. The Russian government directed extensive activity, beginning in at least 2014 and carrying into at least 2017, against U.S. election infrastructure at the state and local level.
See also the other four reports by the Senate Intelligence Committee, linked here (I’ve read parts but not all of them):
en.wikipedia.org/wiki/Senate_Intelligence_Committee_report_on_Russian_interference_in_the_2016_United_States_presidential_election
See also just for interest a hearing of a Senate Judiciary subcommittee: www.judiciary.senate.gov/meetings/russian-interference-in-the-2016-united-states-election
See also the Mueller Report from the Justice Department:
www.justice.gov/archives/sco/file/1373816/download
[pp1-2]
As set forth in detail in this report, the Special Counsel’s investigation established that Russia interfered in the 2016 presidential election principally through two operations. First, a Russian entity carried out a social media campaign that favored presidential candidate Donald J. Trump and disparaged presidential candidate Hillary Clinton. Second, a Russian intelligence service conducted computer-intrusion operations against entities, employees, and volunteers working on the Clinton Campaign and then released stolen documents. The investigation also identified numerous links between the Russian government and the Trump Campaign. although the investigation established that the Russian government perceived it would benefit from a Trump presidency and worked to secure that outcome, and that the Campaign expected it would benefit electorally from information stolen and released through Russian efforts, the investigation did not establish that members of the Trump Campaign conspired or coordinated with the Russian government in its election interference activities.
I’m sure for some people and media, the last clause of the last sentence is the bit that interests them most.
However the rest of the Mueller report does establish in great detail that Russia did interfere in the 2016 election. Not a secret report, and very well publicised.
You’ve nonetheless formed the impression that the idea of Russian interference in 2016 is “largely unfounded”.
Much of this thread is discussing whether the media we consume is giving us the full picture. Maybe your preferred media didn't give you the information you needed on this.