Many people are confused why some things in the Senate require a simple majority and others require 60 votes.
Welcome to the complicated and arcane world of Senate rules and procedure.
Most of the time it works like this: regular legislation will need 60 votes if even one senator decides to filibuster. The 60 votes is actually a vote to invoke cloture. If cloture is invoked with 60 votes it starts the debate clock. In most cases cloture has to “ripen” and that can take a couple days while no more than 30 hours of debate is scheduled ... followed by a vote.
Budget reconciliation is a different critter. Here you only need 51 votes to prevail. But items in a budget reconciliation bill must be ruled germane to the budget process (it’s called the Byrd Rule). Recently the Senate Parliamentarian ruled the Minimum Wage provision in the $1.9 T Covid stimulus bill sent over from the House is not germane — so it’s been stripped out of the bill.
You only need 51 votes for a judicial or executive branch nomination. At one point nominations were filibustered, but the Senate changed that rule.
It’s true that Senate rules can be changed by a simple majority vote. This is why Joe Manchin and to a lesser degree Kirsten Sinema are so important right now. Both have said repeatedly they will NEVER vote to change the filibuster rule or the Byrd rule. It means right now Dems don’t have the 51 votes they need to change the rule.
See, it’s complex. So what I usually say is, “most difficult things require 60 votes in the Senate.”
Hope that helps.