Just use "Chrome Portable 126.0.6478.183" or "Brave Portable 1.65.126" (if you want to run the normal updated Chrome at the same time) just for IG Giveaways and this extension. Both are the last versions before the nagging and forcefully turning off manifest v2 stuff.
close Chrome, and then only start it with this commandline (or as a shortcut): "chrome.exe --disable-features=ExtensionManifestV2Unsupported,ExtensionManifestV2Disabled"