The President, with voting confirmation from the Senate appoints judges to lifetime appointments for any open vacancy at the District Court level, Appeals Court level and obviously the Supreme Court. Many cases don't make it to the Supreme Court. They are one and done at the District Court or they are closed at the Appeals Court. These decisions have an impact on people's everyday life. Trump appointed many District and Appeals Court judges during his term. Some of whom were considered unqualified by the association that grades these lawyers/judges. Others were bigots and super pro life types. These people will serve for the rest of their life. In a 2nd Trump term I would definitely expect him to look to appoint judges who would be loyal to him and not the constitution. A Judge Cannon type. The one who was appointed by Trump, threw out his Classified Documents case and was considered unqualified by many to even be hearing the case in the first place due to the complexity of the case and her not having any real experience.
The President, in conjunction with the Attorney General and voting confirmation from the Senate appoints US Attorneys in every District in the country. Once the new President from the opposing party come in, the President and Attorney General can fire most of the US Attorneys and replace them with his people. Trump famously did this when he became President. In 2020 Trump/Bill Barr fired the US Attorney for SDNY. The US Attorney had prosecuted people close to Trump and Trump himself and his inauguration committee was under investigation in SDNY. It was clearly done to Obstruct Justice. Similar to what Trump did to Comey in 2017. In a 2nd Trump term, Trump would clearly want to appoint US Attorneys, particularly in districts where he think he has criminal exposure, that are loyal to him and not the constitution. People that may be willing to investigate and prosecute whoever Trump tells them to go after. Just like he pushed the Department of Justice to indict Comey and Hilary Clinton but his White House Counsel shut that down because it's an abuse of power and not the President's job. US Attorneys and Assistant US Attorneys can also effect people's day to day life by either showing leniency, being fair, or being un-necessarily strict. This includes when they push for either lenient sentencing or hard sentencing.
The President, with voting confirmation from the Senate also appoints officials to top positions in every federal agency. If you care about climate change, clean environments, etc, then you would want to care who is appointed at the EPA. (Even though the Conservative Supreme Court just weakened the EPA's ability to regulate pollution that crosses state lines and creates smog.) If you care about Small Business, then you would want to care who is appointed at the Small Business Administration. Is it someone that's willing to extend grants, money and opportunities to black people, minorities to start, grow and continue businesses? The same goes with HUD (Federal Housing Administration)
The President, with voting confirmation from the Senate also appoints top military officials. Normally this wouldn't matter, but there's two things that come to mind: Trump wanted to use the actual military against peaceful protestors at LaFayette Square during that George Floyd protest. Since that didn't happen, the National Guard was used. And they tear gassed peaceful protestors so that Trump could walk across the street for a photo op. Very authoritarian move that a President should never do. After Trump lost the election, top military officials were worried that Trump would use the military to help him overturn the election. Because his boy Mike Flynn had told Trump to make the military seize voting machines and enforce Martial Law. Top military officials released a statement saying that the military would not be used to interfere in the election. Trump then fired the Defense Secretary and other top officials in the department, and replaced them with Trump loyalists which led to 10 former Defense Secretaries doing a joint letter in the Washington Post saying the election, there needs to be a peaceful transfer of power and warning against using the military to help overturn the election. In a 2nd term Trump would clearly appoint people that were loyal to him and not the constitution. And if he wants to use the military against citizens, nobody would stop him this time.