from: https://blog.aspyr.com/2018/02/22/performance-alert-macos-10-13-4/
At the 2017 Worldwide Developers Conference, Apple announced that High Sierra would be “the final macOS release to support 32-bit apps without compromises.”
With the next version of macOS after High Sierra, Apple will warn users about 32-bit apps before phasing them out. This notification is one such warning.
We are currently working on updating our most popular 32-bit apps to 64-bit to ensure future playability. The roadmap for releases and updates is currently unknown. This transition does present unique development challenges, and it’s not yet known if every Aspyr game will be upgraded.
To ensure playability of your favorite 32-bit apps we recommend waiting to upgrade to a new MacOS beyond High Sierra until we are able to verify 32-bit functionality.
We are currently unsure how long current 32-bit apps will be playable on future operating systems, or how the gameplay experience will be affected.
Players should know that existing 32-bit apps are not known to affect your Mac’s performance at this time.
This affects the following games on the AppStore and Steam.
BioShock Infinite
Borderlands 2
Borderlands: The Pre-Sequel!
Call of Duty
Call of Duty 2
Call of Duty 4: Modern Warfare
Call of Duty: Black Ops
Call of Duty: Modern Warfare 2
Call of Duty: Modern Warfare 3
Civilization IV
Civilization IV: Colonization
Civilization V
Command & Conquer™: Generals Deluxe Edition
Company of Heroes Complete: Campaign Edition (No longer available for sale)
Doom 3
Duke Nukem Forever
Fahrenheit: Indigo Prophecy Remastered
Geometry Wars 3: Dimensions (No longer available for sale on MacAppStore)
Homeworld Remastered Collection
Prey
Quake 4
RAGE
RollerCoaster Tycoon 3 Platinum
SimCity 4: Deluxe Edition
SimCity: Complete Edition
Star Wars: Empire at War
Star Wars: Knights of the Old Republic
Star Wars: The Force Unleashed
Star Wars Jedi Knight: Jedi Academy
Star Wars Jedi Knight II: Jedi Outcast
The Secret of Monkey Island: Special Edition
The Sims 2: Castaway Stories
The Sims 2: Life Stories
The Sims 2: Pet Stories
The Sims 2: Super Collection
Tomb Raider II
Hey @Sammy are the COD4 mods 32 or 64 bit or are they 'interpreted/script' so going 64-bit won't make a difference?