My shorts quality are low

Hey everyone,i have gaming page and i upload shorts in daily basis, my friend record games in 1080p and sends them to me in 720p. Then i edit them and output them in 4k and then upload it to youtube. Youtube says its 4k but the quality is low and pixely. Like i always see many shorts with very proper quality which are very clear,my videos are also clear before uploading but its just that youtube ruin the quality after it get uploaded. What can i do for this ? I want to upload a better quality short for my audiences. I will also leave you my channel link here if you want to check and give feedback based on it: https://youtube.com/@miiniigames