I would say, hold your guitar however it feels comfortable. The thing most people will do at the start is to rest their guitar on their right leg (if you are right handed).
The reason for this I think is because it just makes it easier to press the chords when you’re starting out as the head of the guitar is within easy reach and not sticking far out to the left.
Sometimes I will rest it on the left leg if I’m playing lead as it gives me easier reach up and down the neck however these rules are NOT written in stone.
I just do what feels comfortable and you should do the same.
When standing up and playing, make sure your strap isn’t too loose and you need to twist your wrist to play the chords.
For beginners, it’s easier to play with a tighter strap so you can reach the chords easily.
How you hold the guitar is not as crucial as some people and teachers make it out to be. As long as you can reach and play the chords easily, you’re on the right track.