Contrary to some of the comments on this, it appears to be the mobile Android version of PUBG. Despite the Snapdragon 820 and 4GB of RAM, you need to consider that you have an old phone at this point (in terms of how far technology has come since the Lenovo Zuk Z2+ released in 2016). It's entirely possible that you are expecting too much out of your phone. The Adreno 530 in that phone is a chip designed with 2015 tech in mind, and although 5 years doesn't seem like a lot of time, it is in terms of phone power.
PUBG is a big, intense game, with a lot of assets to load, and a lot of player connections (~100) to handle. It's very possible that what you're experiencing is just how it is for your model phone. Something newer might be a better answer, and I doubt there's a technical fix that will drastically improve your gameplay experience.