Is it permissible to pray sitting down at work due to lack of space, and is it permissible to combine prayers if it is not possible to perform them on time?

Standing in obligatory prayers is a pillar that is not waived except in case of inability to do so, based on the Almighty's saying: "And stand before Allah, devoutly obedient." So, whoever has an excuse that prevents him from standing, such as illness or a place where he cannot stand, it is permissible for him to pray sitting, based on the Prophet's (PBUH) saying: "Pray standing; if you cannot, then sitting." As for supererogatory prayers, it is permissible to perform them sitting even if one is able to stand, but their reward will be half the reward of one who stands.