You can start here:

https://en.wikipedia.org/wiki/Mueller_report

The report states that Russian interference in the 2016 presidential election was illegal and occurred “in sweeping and systematic fashion”, and was welcomed by the Trump campaign as it expected to benefit from such efforts. It also identifies multiple links between the Trump campaign and Russian officials,about which several persons connected to the campaign made false statements and obstructed investigations. Mueller later stated that his investigation’s findings of Russian interference “deserves the attention of every American”.

And here:

https://www.pbs.org/wgbh/frontline/article/the-mueller-investigation-explained-2/

According to Barr, the special counsel found two main Russian efforts to meddle in the 2016 election. The first was through the Internet Research Agency, a Russian organization that conducted “disinformation and social media operations in the United States designed to sow social discord, eventually with the aim of interfering with the election.” The second was the Russian government’s hacking operations “designed to gather and disseminate information to influence the election.”

And here:

https://investigaterussia.org/media/2018-03-18/cambridge-analyticas-russia-connection

Mr. Nix is a director of SCL Group, a British political and defense contractor, and chief executive of its American offshoot, Cambridge Analytica, which advised the Trump campaign. The firms’ employees, who often overlap, had contact in 2014 and 2015 with executives from Lukoil, the Russian oil giant.
…
Christopher Wylie [whistleblower], who helped found Cambridge Analytica and develop the company’s voter-profiling technology, said Lukoil showed interest in how the company used data to tailor messaging to American voters.
…
Though Lukoil is not state-owned, it depends on Kremlin support, and its chief executive, Vagit Alekperov, has met with Mr. Putin on a number of occasions. Reuters reported last year that Lukoil and other companies received instructions from the state energy ministry on providing news stories favorable to Russian leadership.

And here:

https://en.wikipedia.org/wiki/Russian_interference_in_the_2016_Brexit_referendum

The report discussed more broadly Russian interference in British politics, including an extensive “laundromat” of Russian investment into the United Kingdom often connected to the Russian state and the Putin-linked elite. It discussed the likely effect on politics and that many members of the House of Lords have business interests in Russia.
…
In September 2020, the Electoral Commission raised concerns about Russia-linked donations to the Tories that occurred prior to the Brexit referendum. In October 2021, the Pandora Papers revealed more information about the potentially Kremlin-linked donations and multiple others.

And if you still have doubts that it’s a concerted and deliberate strategy that’s an explicit part of Russia’s internal policies, try this:

https://en.wikipedia.org/wiki/Foundations_of_Geopolitics

The textbook advocates a sophisticated program of subversion, destabilization, and disinformation spearheaded by the Russian secret services.

And this:

https://www.bbc.com/video/docs/series/10141108

(That last one didn’t used to require a subscription to watch… you might be able to find it on the high seas)

Edit: bonus Putin Ordered Kremlin to ‘Destroy NATO and EU From Within’