This is a press release from the Complutense University of Madrid (UCM) on June 30.
https://www.ucm.es/una-publicacion-de-la-ucm-confirma-que-los-enjuagues-bucales-con-antisepticos-podrian-desempenar-un-papel-preventivo-en-la-transmision-de-la-covid-19
It starts with a heading that goes like this:
“Una publicación de la UCM confirma que los enjuagues bucales con antisépticos podrían desempeñar un papel preventivo en la transmisión de la COVID-19”
"A UCM publication confirms that antiseptic mouthwashes could play a preventive role in the transmission of COVID-19.”

Here the word "enjuague" can be translated as “gargle,” the same as another Spanish word “gárgara.” Here are the differences:
Enjuagar: “To wash the mouth and teeth using an appropriate liquid. Noun: enjuague.” This is probably “rinse” in English.
Gárgara: “The act of keeping some liquid in the throat without swallowing, exhaling air with the mouth facing upward, and making a sound like water boiling.” This is “gargle” in English.
In Japanese, the former would be “bukubuku ugai” or “kuchukuchu ugai”, in other words, rinse, while the latter would be “garagara ugai”, wouldn’t it. In Spanish, English, and Japanese it’s “gárgara,” “gargle,” and “garagara,” so it seems these words come from the sound. Perhaps you could distinguish them like this: Washing or sterilizing of the mouth is “kuchukuchu ugai” (mouthwash) and washing or sterilizing of the throat is “garagara ugai” (gargle).

Well, setting aside the language exploration, this research by the Etiología y Tratamiento de las Enfermedades Periodontales y Periimplantarias (ETEP) Group, or the Etiology and Therapeutics of Periodontal and Peri-implant Diseases Group, at the Faculty of Dentistry at UCM was published in the German academic journal Clinical Oral Investigations as the results of their analysis of academic papers registered up to April 30, 2020 with the keywords SARS-CoV2 (the novel coronavirus), COVID-19 (the novel coronavirus infectious disease), oral cavity, and antiseptic found on PubMed https://pubmed.ncbi.nlm.nih.gov/, the medical database maintained by the US National Library of Medicine. The title: Is the oral cavity relevant in SARS-CoV-2 pandemic?
The original English text is here: https://link.springer.com/content/pdf/10.1007%2Fs00784-020-03413-2.pdf

Text summary (PDF): Is the oral cavity relevant in SARS-CoV-2 pandemic?

Their conclusion was: “Antiseptic mouth rinses, such as those containing cetylpyridinium chloride or povidone-iodine, may be able to decrease the severity of COVID-19 by reducing oral viral load in infected subjects and decreasing the risk of transmission by limiting viral load in droplets, generated in normal life, or in aerosols, produced during dental procedures. Well-designed clinical and preclinical research must be conducted to support these hypotheses.”

This is a video that the paper’s authors broadcast live on May 28. They speak in easy-to-understand English.
https://www.youtube.com/watch?v=YU8xeQlqixQ

If the main route of infection is droplets or contact, there is a high risk of infection among dental practitioners and personnel, who carry out treatment of patients’ mouths, so in terms of reducing that risk, use by patients of mouth rinses before treatment may be beneficial in preventing other infections, not just COVID-19. Given the difficult circumstances of the COVID-19 crisis, perhaps this research carries with it the desire to make consultation and treatment for the people who work in dental care even a little safer, and also to make things safer and more reassured for the people receiving those consultations and treatments.
Being a measure against COVID-19, I think this information might be of benefit even for people with no connection to dental care.

It is also said, however, if you use a mouth rinse that contains antiseptic every day for a long time, you keep your mouth too clean, and bacteria that usually live in your mouth are replaced by bacteria of a different kind, which is actually dangerous. Maybe the problem with your bacteria being replaced would be OK if you use toothpaste with cetylpyridinium chloride (CPC), which is effective in preventing periodontal disease when you brush your teeth in the morning and evening, and when you're done, you do a kuchukuchu ugai and rinse your mouth using tap water containing chlorine, which has an antiseptic action (the antiseptic used by the Madrid City Waterworks Department is chloramine).