To upgrade Magento version 2.3.4to 2.3.5 follow this steps:

Step 1 – enable mainenance mode

php bin/magento maintenance:enable

Step 2 – composer require

composer require magento/product-community-edition 2.3.5 --no-update

Step 3 – update composer

composer update

Step 4 – cleanup before upgrade magento

rm -rf var/* pub/static/* generated/*

Step 5 – upgrade and static content deploy

php bin/magento setup:upgrade
php bin/magento setup:static-content:deploy -f

Step 6 – compile, reindex and clean cache

php bin/magento setup:di:compile
php bin/magento indexer:reindex
php bin/magento cache:clean
php bin/magento cache:flush

After above, check your Magento version typing command:

php bin/magento --version

And disable mainenance mode

php bin/magento maintenance:disable