@2alamoony is not a matter of anything having a problem or needing to be fixed. I've done a couple of quick searches and you are asking about a feature that the phone does not have: the Xperia 10 III is advertised with a single speaker.
On GSMarena, scroll down to "sound" to see the difference: https://www.gsmarena.com/compare.php3?idPhone1=10712&idPhone2=10851&idPhone3=10698
Loudspeaker: "Yes" (£400 Xperia 10) vs "Yes, with stereo speakers" (for the £900 Xperia 5 and £1200 Xperia 1)
This means that it only has a speaker at the top, for use as a phone. It will still output sound when you rotate the phone into landscape - the normal orientation for TV's, etc (to watch a video/Youtube/movie), but only from that one speaker.
In case this isn't clear:
If you rotate the phone 90deg anti-clockwise, into landscape (to watch a video/Youtube/movie), it will only have a speaker on the left, no sound on the right at all.
If you rotate the phone 90deg clockwise, into landscape (to watch a video/Youtube/movie), it will only have a speaker on the right, no sound on the left at all.
Sound only coming out of that one side is expected, not a problem.
I know that dual/stereo speakers are a standard feature even on a lot of lower end devices from the budget manufacturers (e.g. the £220 OnePlus NORD N10 "Loudspeaker: yes, dual"*), but the premium manufacturers tend to only add this on their higher end phones: so you will find the same lack of of stereo speakers for the £250-£320 Galaxy A71 ("Loudspeaker:yes") vs the £550-£575 Galaxy S21 ("Loudspeaker: Yes, with stereo")
*in the case of the OnePlus NORD N10, it's actually full left+right stereo when you are in portrait AND when you're in landscape (I think there are actually four speakers!). They really aren't very loud, but it makes anything on the speakers feel much more natural and immersive: along with the £100+ saving, it was one of the key reasons I went for that over the Xperia 10 for my son.
Just for clarity I love the Sony phones: my wife and I have have Sony's for the vast majority of the last 10 years, so I am loyal to the brand IF Sony are selling any compact phones that meet the specs I'm after, but I wasn't willing to spend nearly £700-£800 on last year's Xperia 5 II just for stereo speakers for my 10yr old.... the plan was to let him have my wife's XZ2C and she could have the upgrade, but Sony keep delaying the "April 2021" Xperia 5 III, so we had to buy another device.... and now that my XZ2C is falling apart (not the phone's fault: 3 years of HARD use, to be fair!), but I'll probably have to buy something similar until SONY get sharper with their releases.
