YouTube's keyboard shortcuts for volume control are the arrow keys. Pressing Up will increase the volume in five percent increments; pressing Down will decrease the volume by the same amount.

https://www.makeuseof.com/tag/3-ways-control-youtube-video-volume/#:~:text=YouTube's%20keyboard%20shortcuts%20for%20volume,volume%20by%20the%20same%20amount.

Read some of these methods and see if you find one that works for you..☺☺☺

https://www.google.com/search?q=how+to+control+volumn+of+youtube+videos&sourceid=chrome&ie=UTF-8

Well, after a new reboot of your computer and with no programs or ap's loaded, click the speaker icon in the lower right corner and set all the volume controls to the max, 100%.

That's the last possible option. Then after you are on the YouTube website check those speaker settings again. ☺☺☺

Well, all that's left is your audio device and driver, like Realtec is the audio device on my laptop.  Right-click the speaker icon again and select each of the options under "Troubleshoot sound problems".

If that fails you need to take your computer to a repair shop and let them troubleshoot and repair the problem.