See: ‘Youtube playback error - #14 by fanboynz’
UPDATED Sunday, May 24th:
See: ‘Youtube video playing problem - #2 by 289wk’
Test > Go to ‘https://www.youtube.com’ and Allow all Trackers & Ads in Brave Site-Specific Shields - click the Brave Lion icon adjacent to the right end of the URL address field.
Try: An on-demand update check of the Brave Browser installed components. Visit brave://components/ in Brave, go down the list and press all of the “Check for update” buttons.
Consider the following test … Create a new user Profile for only viewing YouTube videos and not signing in to anything of the Google Eco-System:
Menu → More tools → Add profile
When creating:
- Make no appearance adjustments other than to set user profile color at
brave://settings/manageProfile. - Do not import anything.
- Do not add any extensions.
- Do not make any adjustments to content filtering at
brave://settings/shields/filters. - Do not allow/enable any Brave Browser “bells and whistles” such as Brave Rewards, Brave Talk, etc.
Use Brave Browser Private Windows.
Also, for some unknown reason, Brave has changed the former “tune” icon that was adjacent to the left end of the URL address field … to now be a right-aimed arrowhead … when using YouTube.
“Tune” icon: 
IF you click on the “arrowhead” icon at YouTube, you will still get the pop-down menu that includes the ‘Reset permissions’ button.