Due to Olympics and Paralympics preparations, the regular place where you got the shuttle bus to Beauvais airport from Paris, at Porte Maillot, will be closed as of tomorrow May 10 through presumably the end of the Paralympics (no end date is specified as of yet, but keep in mind the Paralympics closing ceremony isn’t until September 8).
To get to Beauvais airport from Paris as of tomorrow (or vice versa), you will have two options:
One: from Metro stop Saint-Denis Universite on the line 13: there will be 80 daily round trip shuttles. you can buy tickets on the bus or reserve ahead. They will also honor pre-purchased tickets that were for shuttles from the Porte Maillot site.
Two: from La Defense (Line 1, RER A, etc etc). HOWEVER — there will only be 20 shuttles daily, and you MUST pre-reserve.
Find the information on the temporary changes here on the Beauvais airport website:
https://www.aeroportparisbeauvais.com/en/access-parking/paris-airport-shuttle
(The same information obviously goes if you are arriving INTO Beauvais airport and coming into Paris. If you take their shuttle, your options are to arrive at St Denis-Universite on the line 13 (more frequent daily schedule) or to La Defense.)