How can I fix lag/desyncing issues?

I've been getting hard lag/desyncing issues in wynncraft lately at completely random. I've checked my internet and it's not showing any issues (I've speedtested my internet during these issues and it's getting a constant 90-100mbps) and I'm guessing it's not a server issue since no one else seems to be complaining. I've tried going with both fabric/forge wynntils and without it and nothing seems to change between versions (I've tried mc 1.12 and 1.19.3). The only mods I'm using in forge/fabric are optifine and wynntils. Any way I can fix these issues?

Update: I've now also tried a lot of other stuff. Reducing particle effects, no smooth lighting, playing without any other programs running on the background, increasing minecraft ram usage from 2GB to 4GB. I should also clarify a few other things: The lag issues started a month ago (around mid august) and haven't stopped since, I am using an ethernet directly connected to the router with 90/100mbps, my processor can 100% run wynncraft, I have 16GB of ram, I'm not using any shadders (or other asthetic rescourcepacks), none of my other games OR minecraft servers have been having any lag/latency issues and I live in southeast europe.

 

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