[4cao]

大陸 /dàlù/ 'mainland' is used but often pejoratively. It's a politically charged issue as this article from a pro-KMT newspaper can attest: https://www.chinatimes.com/newspapers/20180520000567-260109

對岸 /duì àn/ 'opposite [side of the Taiwan] Strait' is a neutral term coined specifically to avoid the controversy.

If talking about politics, another neutral way could be to just say 北京 /Běijīng/.