Amazing work! The background adds the *aesthetic* to the cute Riolu

The flag looks white-ish. Does this mean he/she is surrendering?

I can't remember since I made this in 2018

While the "flag" looks kinda light-grey, it does kinda look like a makeshift "white flag" made from an old piece of cloth (this is a popular depiction of white flags in media because the hero is pinned in the midst of battle and they have to use whatever white-ish piece of cloth and tie it to a stick to by them some time to negotiate or distract the enemy. The "flag" depicted here looks like a shirt or cloak tied to a bamboo stick in a hurry, very emblematic of that trope.) The pose here doesn't really look like a "surrender pose" though. It looks like a brave, triumphant pose. So it's kinda giving off mixed-messages. Otherwise it IS very well drawn though.