"Also, I know everywhere it says "April 15" is the deadline to do "the correction" but if I'm not mistaken, that's now May 17th because of the extended deadline, correct?"

You need to sign up for IRS e-newsletters. This came out (they come to you by email) last week:

"Remove Excess Salary Deferrals by April 15, 2021

The total of all salary deferrals a participant makes to various retirement plans – including 401(k), 403(b), SARSEP and SIMPLE IRA plans – is limited to $19,500 (plus an additional $6,500 if age 50 or over) for 2020.

If an individual defers more than this limit for 2020, the excess deferral amount plus earnings must be distributed by April 15, 2021. Excess salary deferrals not withdrawn by April 15 are taxable in 2020 and again when withdrawn. The date to remove excess salary deferrals has not been extended.

Individuals who made salary deferral contributions to two or more retirement plans in 2020 may be most at risk for exceeding the deferral limit. Use our Interactive Tax Assistant to help determine how to correct excess salary deferrals."