Hey hamidrehman,
Thanks for using Apple Support Communities! I understand you're running into an issue with your iPhone not charging fully. I definitely know how important it is to be able to charge your iPhone without issue, and I'm happy to help.
To start, ensure you're using an Apple branded charger when charging your device. Also, in Settings > Battery > Battery Health, try disabling Optimized Battery Charging, and testing if you're able to charge past 80% at that point.
If this behavior doesn't continue with that turned off, go ahead and turn Optimized battery charging back on (if you'd like) and test one more, as this feature shouldn't prevent from your device to changing past 80% but you may notice a delay after hitting that 80%. You can see more about your iPhone battery here: iPhone Battery and performance
You mentioned this issue has been happening since right after you got your device, was your device restored from a backup made from a different iPhone?
Thanks again, and have a great day!