The documentation you will find online is always for the latest release of MATLAB. You are likely using a release prior which did not have this option. Prior to the 'Display' option the same could be achieved by the following:
opt = optimoptions('fmincon','Display','off'); % Get fmincon default options and turn display off
opt = struct(opt); % Convert to structure
data = randn(200,1); % Random data for fitting
model = egarch(1,1); % Create model
fit = estimate(model,data,'options',opt); % Pass options argument
This will not work in current versions of MATLAB and it is recommended to use the Name-Value arguments for the estimate function.
