If you've picked up this game but had the issue of an unstable FPS.
This guide will help you FIX This issue without having to change the version of the game

This fix is really simple,open the game and turn off V-Sync.You also wanted to turn down the resolution to your desired amount.This fix may cause Screen tearing due to the V-Sync setting.This may also not fix the issue(Because it didn't work for me) But there is another option.

This option will most likely fix this issue that Team17 Has not fixed yet.Enter the Windows Security App,and click "Virus And Threat Protection". Next,Scroll down until you see "Virus & Threat Protection Settings"Scroll down to "Exclusions"
And then click "Add or remove Exclusions". Add a folder and go to C:\Program Files (x86)\Steam\steamapps\common\WormsWorldParty and select it.This will fix this issue i had since i got this game.

A fix i see a lot is to go and use the first version of the game.This will fix the lag spikes but add more issues.The Menus will no longer be in a crispy native resolution like this. But instead in a low 640x480 resolution, similar to Worms Armageddon.This
may not seem like an issue except the fact that after a custom multiplayer round the game bugs out and this may happen .Another thing that may happen is a locked 30 FPS. On the newest version the game will 60 fps or more while in older version the game will run at a locked 30 FPS.

I hope this guide helped out anyone who wanted to play this with a more stable fps.