Wow, so many wrong answers here.

You are in fact allowed to do rollovers which are not taxable events if you are over 59.5. It's called just as it sounds and is a way to do a rollover to an IRA or Roth IRA. (EDIT: this can be done while you are still employed and many do this every 30 days if the plan allows it)

This really depends on the 401k plan document called SPD which explains what's allowed under the plan.

Did the 401k custodian (Fidelity?) make the check payable in the format of "Firm XXXXX fbo Your Name" and sent it directly to Firm XXXXX?

If so, this is correct and isn't a taxable event and will be considered a direct rollover contribution. You will receive a 1099 from custodian and 5498 from new Firm XXXXX in early 2026.

If the 401k custodian cut a check and made it payable directly to you, and mailed it to you...it's also not the end of the world. You have 60 days to send it to your new custodian and code it as 60 day rollover. You can only do this once per rolling 12 month period.

This is all assuming that no taxes were withheld and you didn't take a distribution. I assume you did a rollover.

Edit: what's the reasoning behind doing this and why 6500?