It really depends on the flux, even modern fluxes have a range of toxicity. The only way to know is to check the MSDS. I use Канифоль/rosin flux as well and us

It really depends on the flux, even modern fluxes have a range of toxicity. The only way to know is to check the MSDS. I use Канифоль/rosin flux as well and use a fume extractor. Rosin flux is the most common for flux-cored solder in my experience. But a few times a year is unlikely to be an issue, soldering health effects are in people who do it for work.