Learn Danish: Testpanelet synes at menuen er knap så brugervenlig i år. - The test panel thinks that the menu is not quite as user-friendly this year.

Knap så literally means 'barely so' or 'not quite as' and acts as a downscaler. When placed in front of brugervenlig (user-friendly), it means the menu is less user-friendly than before. Danes frequently use knap så + adjective as a polite understatement to simply mean 'not very'.

Why is synes used for 'thinks' instead of tror?

The verb synes is used to express a subjective opinion based on personal experience. Because the test panel has actively used the menu and evaluated it, this is their opinion. You would use tror if they were just guessing a fact or stating a belief without having tested it.

Would the adjective brugervenlig change if the panel were evaluating a different noun?

Yes. Adjectives in Danish must agree with the gender of the noun they describe. Because menuen is a common gender noun (en word), brugervenlig takes no ending. If the panel were talking about a neuter noun like et system, it would need a -t at the end: systemet er knap så brugervenligt.

Could we use dette år instead of i år for 'this year'?

You should stick to i år. In Danish, i år is the standard, fixed expression for 'this year', just like i dag is used for 'today'. Using dette år isn't grammatically wrong, but it sounds overly formal or awkwardly emphatic in a standard sentence like this.