I'm not a virologist, but I have studied viruses and used them to study other things, hijacked their function, etc.
At one job we were studying a challenging membrane protein - a calcium transporter called orai1. This protein is made of 6 subunits that arrange themselves in a hexagon embedded in the cell membrane, with a central Ca++ pore. We were trying to make antibodies against it, but it is incredibly challenging to try to solubilize a membrane protein with higher order structure in a way that preserves how it looks in nature.
A colleague in Denmark had a plasmid from grad school containing the gag/pol gene from a murine leukemia virus. The proteins coded for in this gene are necessary and sufficient to produce viral particles that bud off from the cell membrane of a transfected cell. We used HEK293 cells that were already overexpressing Orai1 and I purified the virus-like particles using an ultracentrifuge. These VLPs were decorated on the surface with intact Orai1 and we were able to use them to get spectacular antibodies made.
At another job I worked with the AAV virus. We hijacked this one such that we could replace most of its tiny genome with e.g. a piece of DNA that coded for an ADAR guide RNA. The guides were designed to bind to a defective mRNA and could effectively change an 'A' to a 'G' in that mRNA. In the case of e.g. certain types of muscular dystrophy, changing the 'A' in a premature stop codon to a 'G' resulted in full length dystrophin being made and the potential for a kid with that genetic disease to live a more normal life.
I did analytics on these vector preps that involved using ultracentrifugation to separate empty capsids (most of them) from full capsids that contained our DNA payload. We ran a fairly cutting edge mass spec technique that is able to literally weigh each capsid to observe the fraction with payloads vs. empty, and also even partial (smaller) payloads. We could also study the mass distribution of the capsids themselves since they are made up of 3 proteins all of slightly different masses and the 60 subunit icosahedrons assemble stochastically and therefore the viral particles have different ratios of the 3 structural proteins - hence you get a distribution of empty capsid masses.
My colleagues put these preps on cells and were able to measure mRNA editing in the cells using next generation sequencing.
So here, from a bunch of biophysical first principles, I was able to see evidence of viral structure and function as defined as being able to get into a cell and interact with the cellular machinery.
Be careful of people who tell you viruses don't exist. Sometimes in an information war, adversaries will plant ideas that are picked up and espoused by people who are otherwise sharing uncomfortable truths, in order to discredit them and lower the impact and reach of their message.