under kitchen sink

I bought a new garbage disposal and sink and decided to install them myself. The sink and garbage disposal are good. I’m trying to get the drain pipe fixed. I have added before and after pictures. Can someone take a look and let me know if I’m doing the right thing? Appreciate your advice...

Can someone please tell me if there is a different way to pipe this? Sometimes it drains fine and sometimes it’s suuuper slow. I did it myself so please go easy on me! First time homeowner looking to save some money ;)

My house was built in 2011 when I bought it new. I started having sewer smell coming from under the kitchen sink cabinet about 3 years ago. No smell from the sink or dishwasher. I deep clean them regularly. I also don’t have food debris in the dishwasher. I can’t figure out where the sewer...