For your visa demand:
https://france-visas.gouv.fr/en/web/france-visas/welcome-page
If you need a participation letter to get a visa for France, please contact the Conference Secretariat. Just specify the information requested for your visa demand (personal address, passport number).
About vaccination:
https://www.interieur.gouv.fr/covid-19-international-travel
Sanitary rules:
The vaccination schedule is considered complete 28 days after receiving one dose of Janssen vaccine, seven days after a second dose of other vaccines approved by the European Medicines Agency (namely Pfizer/Comirnaty, Moderna, AstraZeneca/Vaxzevria/Covishield) and, for persons who have received all the required doses of a WHO-licensed vaccine not approved by the European Medicines Agency, seven days after receiving an additional dose of a duly approved mRNA vaccine.
Since 1 February 2022, in order for their vaccination schedule to continue to be recognized as complete, persons aged 18 years or older wishing to enter French territory must have received a booster dose of messenger RNA vaccine no later than nine months after receiving the last mandatory dose.