Exit polls this year included early voting and mail in voting in most cases and anyway, they were all shifted blue, which makes no sense given the Republican-heavy election day voting. Furthermore, exit polls matched pre-election polls almost perfectly this year:
Pre-election polls: Biden +8.5
Exit polls: Biden +7.8
The .7 difference is within the margin of error.
In most states the match between pre-election polls and exit polls was also excellent.