Great Lord

Ok, thank you so much for investing your time in this to help me out. 😃 I am also considering using Sodium, Phosphor and Lithium mods when they are released to get even better performance.

@violine1101 The minimum requirements for Minecraft stated in the website is Intel core i3 3210 @ 3.2 GHz, 4 GB RAM and Intel HD 4000 graphics. My PC does meet the minimum requirements!

Ok, here you go(this was the original world last saved in 1.16.5, before upgrading to 1.17):-

https://drive.google.com/file/d/1HRGCQNroc4BZTtDRbKYBBUW5TYhfElqm/view?usp=sharing

MC-228302 doesn't seem to directly describe my issue, because I didn't break any shut trapdoors, that might result in lag(if I understand this correctly). Anyways, here's the original zip file of my 1.16.5 world(before it was upgraded to 1.17):-

Edit: It doesn't let me upload my world, because the maximum size limit is 10 mb.

So, someone made a comment asking me if MC-219639 relates to my issue, and then promptly deleted their comment. It seems like yes, it does relate to my issue. Here's the link to MC-219639:-

MC-219639 Performance loss after using OpenGL 3.2 core profile - Jira (mojang.com)

Edit: It looks like MC-219639 might not relate to my issue, as per ampolive.

I deleted all the datapacks from my world's datapacks folder and opened the world in 1.17. Still lagging like before.

Here you go:-

@SomeonePLaysMC Ok, so I did exactly what you said. My world was running smoothly till Pre-Release 2. After that, it gets interesting. I will break it down version by version after Pre Release 2:-

Pre-Release 3: Little laggy, not as bad as 1.17 but still a bit unplayable.

Pre-Release 4: Still laggy, but less lag than Pre Release 3, fairly playable.

Pre-Release 5: Unbearable lag, just like 1.17.

Release Candidate 1: Unbearable lag, just like 1.17.

Release Candidate 2: This one performed a little bit better.

1.17: Unbearable lag again.

@SomeonePLaysMC Ok, so I did what you said. I upgraded my 1.16.5 world to snapshot 21w20a(because loading of old worlds was disabled in 21w14a). And, my game was running perfectly in 21w20a! However, when I further upgraded it from 21w20a to release 1.17, the game was stuttering, but this time it was running a little bit better than last time when I directly upgraded my world from 1.16.5 to 1.17. However, the lag is still unbearable in release 1.17, albeit a little bit less.

@SomeonePLaysMC Good suggestion, but new worlds created on 1.17 are running buttery smooth, as is the existing world on 1.16.5. I am only facing this issue when upgrading existing 1.16.5 worlds to 1.17.