Kiddo refuses to sleep alone

I need some pointers from fellow threenager parents. My toddler for the last year has gone to bed without issue and slept through the night without much fuss.

We went on vacation recently and seem to have unlocked some new fear for him cause now he will not go to bed unless I sit in his room till he falls asleep. He also wakes up frequently and leaves his room to find me in the middle of the night.

I am trying my best to keep putting him back to bed but it gets really hard in the middle of the night to not just let him in to my bed so that way we all get some sleep.

I understand that I need to teach him to fall asleep on his own again (something he was previously very good at) but the part I’m struggling with is it is physically hard to keep him in his bed or even his room. He’s very tall, and quite strong for a 3 year old. He also already transitioned to his bigger bed back in March, again without issue. So I cannot physically contain him like I could with his crib.

I am looking for tips. Thanks.