There are no reputable scientists who believe viruses do not exist. There are a handful of nutritionists who are self-promoting their books by suggesting science has been wrong for all these years and viruses do not exist. They have corrupted the conversation about viruses and polluted the minds of those with little understanding of modern virology.
A good starting point to learn about viruses is to go to a website which debunks all these cranks with hard science.
Fortunately, a researcher with close ties to the scientific community has produced a number of essays which debunks these cranks claims and gives hard scientific evidence which will improve one’s understanding of modern virology.
Frank Visser, The Corona Conspiracy: Combatting Disinformation about the Coronavirus
Part 1: Corona, Oxygen, 5G: The Paranoid Worldview of David Icke, April 2020
Part 2: Debunking Andrew Kaufman's Virus = Exosome Hypothesis, May 2020
Part 3: We Need to Talk about Exosomes, May 2020
Part 4: Why Viruses Are Not Exosomes, June 2020
Part 5: The Alternative Facts of Virus Denialism, June 2020
Part 6: The Subtle Science of Whole Genome Sequencing, June 2020
Part 7: Stefan Lanka's Vanishing Virus Act, July 2020
Part 8: Coping with Corona: The Cautious vs. The Reckless, July 2020
Part 9: Andrew Kaufman's Take on the Pandemic That Wasn't, July 2020
Part 10: Between Alarmism and Denialism, August 2020
Part 11: David Icke and the Method in the Madness, August 2020
Part 12: How the Coronavirus Conquered the World, August 2020
Part 13: To Test or Not to Test, That's the Question, August 2020
Part 14: Pandemic, Infodemic, Scamdemic, Plandemic?, August 2020
Part 15: The Chromosome 8 Bombshell Evidence Canard, August 2020
Part 16: What's Up With These Koch's Postulates?, September 2020
Part 17: Was the SARS-CoV-2 virus created in a lab?, September 2020
Part 18: QAnon, When Conspirituality Meets Politics, September 2020
Part 19: Thomas Cowan and "The Myth of Contagion", October 2020
Part 20: PCR-Gate: A Storm in a Petri Dish, December 2020
Part 21: David Icke: 'QAnon is a Psy-Op, a Scam!', January 2021
Part 22: The Million-Dollar Question About COVID-19, January 2021
Part 23: 'The SARS-CoV-2 Coronavirus Has Never Been Isolated', February 2020
Part 24: PCR-Gate 2: When Lockdown Skeptics Pose as Experts, February 2021
Part 25: The Unholy Alliance of Corona Conspiracy Theorists, March 2021
Part 26: Twitter Review of the "COVID-19 Myths" Webinar, May 2021
Part 27: David Icke Shouts Out: 'There Is No Bloody Virus!', June 2021
Part 28: Stefan Lanka's Counterfeit "Control Experiments", June 2021
Part 29: Where Are All These PCR 'False Positives' Anyways?, June 2021
Part 30: Is SARS-CoV-2 the Phantom of the COVID-19 Opera?, June 2021
Part 31: Andrew Kaufman and the "Fake Delta Variant", July 2021
Part 32: Where's the Control Experiment Protocol, Stefan?, September 2021
Part 33: PCR-Gate 3: The Debate About PCR Never Really Happened, October 2021
Part 34: Thomas Cowan and the Spell of Corona, November 2021
Part 35: Samantha Bailey and 'The COVID-19 Fraud', December 2021
Part 36: SARS-CoV-2: Lab Leak or Natural Origin?, December 2021
Part 37: Jorn Luka Goes 'Seriously In-Depth with David Icke', December 2021
Appendix 1: Fifteen Facets of the SARS-CoV-2 Virus, June 2021
Appendix 2: Who's Who in Corona Conspiracy Country, June 2021
Appendix 3: My Corona Conspiracy Twitter Contacts, July 2021