beginner in SEO having hard time

im complete new with SEO but somehow i managed to make it work for a while but suddenly something happened and i don't know hot to fix it...
used to rank for my keyword on the first page on google and i was making some money and i thought it was that easy :( and started to do some improvements as adding more products but it ended up messing everything ive had this problem before but im unsure how can i fix it or avoid it, my first time i just waited and gave it time and it started to show on the first page on google but now its not some told me that bcs of google core update.

in my Performance chart it shows the same position ranking of 30-20 and its stable even tho the reach and clicks are low

ranking went from first page on google to the 3rd page on google

disclaimer: please don't bully me bcs im new to SEO and im not here to disrespect any of your hard work on SEO i just wanted to try and now im in love with my website and how it came together
im from 3rd world country and i cant hire specialist or ever hire someone to do my shopify website design ive made everything from 0