I believe that the worst case scenario, with no cheating by the Republicans, is that Biden will get 290 electoral votes. (270 wins it).
That is with Biden losing Florida, Ohio, both Carolinas, and Iowa.
If he also wins Iowa, North Carolina, Ohio, Florida (all possible), he gets 358. This is a bit extreme but possible. If he gets Georgia (which is on the table) Biden gets 373. For the record, Texas would put Biden at 412. Not likely but we always need to visualize a blue Texas. Someday….