Hi Josefine

I haven't tested this, but maybe it makes a difference it only run on RuntimeLevel.Run?

public class Bundle : IComponent
{
    private readonly IRuntimeState _runtimeState;
    private readonly IRuntimeMinifier _runtimeMinifier;

    public Bundle(IRuntimeState runtimeState, IRuntimeMinifier runtimeMinifier)
    {
        _runtimeMinifier = runtimeMinifier;
        _runtimeState = runtimeState;
    }

    public void Initialize()
    {
        if (_runtimeState.Level != RuntimeLevel.Run)
        {
            return;
        }

        _runtimeMinifier.CreateJsBundle("inline-js-bundle",
            BundlingOptions.NotOptimizedAndComposite,
            new[] { "~/scripts/myScript1.js", "~/scripts/myScript2.js" });

        _runtimeMinifier.CreateCssBundle("inline-css-bundle",
            BundlingOptions.NotOptimizedAndComposite,
            new[] { "~/css/mystylesheet.css" });
    }

    public void Terminate() { }
}

public class MyComposer : ComponentComposer<Bundle>
{ }

It seems if UpgradeUnattended is enabled the Runtime level will use Run instead of Upgrade.

https://docs.umbraco.com/umbraco-cms/fundamentals/setup/upgrading#boot-order

For existing projects UpgradeUnattended was opt-in, but it seems this recently has changed, so it will be enabled by default in new projects.