What is the maximum number of columns allowed in a table?

for Oracle 11g :

1000 Columns per table

32 columns per index

Logical Database Limits:

https://docs.oracle.com/cd/B28359_01/server.111/b28320/limits003.htm#i288032

A limit of 1,000 columns per table applies for versions 8i, 9i, 10g, 11g, 12c, 18c and 19c.

Prior to that, Oracle 7 had a 254 column limit.