I tried installing a site I developed on my work mac (high sierra), pushed to its repo, pulled it down at home on my mac (mojave)and on running composer update get this displayed in my terminal:
Seems you have upgraded Yii Framework from version 22.214.171.124 to 126.96.36.199.
and in the browser get this
PHP Warning – yii\base\ErrorException Declaration of craft\web\twig\Environment::compileSource(Twig_Source $source) should be compatible with Twig\Environment::compileSource(Twig\Source $source)
I tried deleting the vendor folder and running composer install but get the same, however when I delete all database tables and allow craft to reinstall it's fine (albeit no content!!!) I have no idea how to resolve this, any tips appreciated!