Bigfile in oracle 12 is full with 120G
ORA-01652: unable to extend temp segment by XXX

This isn't about your 120GB bigfile data tablespace at all.
Your TEMP tablespace isn't big enough to handle whatever sorts or temporary result sets are created by the queries that are being run in your database. If it can't autoextend, then it is probably because you have filled up the disk drive and you don't have room for more, or because the TEMP tablespace data file(s) have reached the maximum size allowed by the file system (typically 32GB each).
If you still have space available on the file system holding your TEMP tablespace, then add one or more more files to the TEMP tablespace. If the partition is completely full, then work with your system and/or storage administrator to determine how to enlarge the file system or where else you could place additional data files.