Some televisions lose access to services because the manufacturer stops updating the sets to meet new requirements.
https://conversation.which.co.uk/technology/smart-tv-samsung-youtube-app/
I can find no recent posts from other people with Technika televisions having the same problem as you. You could try resetting your television - press the MENU button on the remote and go to the SETUP menu. Then select the RESET TO DEFAULT option and confirm, or check the manual on how to do this for your particular model.
If you still can't get YouTube to open consider buying an Amazon Firestick or similar from around £30 - this should give you YouTube and other apps.
Amazon.co.uk User Recommendation