ooh yes, I soo much need this.  

Sometimes there is a forum question, and I know I have answered it before, but it takes me maybe 15 minutes to scroll through to find the exact answer.

I appreciate the idea because it significantly improves the process of finding the correct information in less time.

Oh and I think I misread your idea a little bit, If filtering is worked on, I would like slightly more :

Especially on Activity tab, but maybe also on Achievement tab, I would like to also have a search input to search the title / content of the achievement or activity.

Both seem reasonable.

I support the idea!

Our Achievements section is overwhelming for highly active members. Adding a filter, like in the Activity tab, would make it easier to navigate and find specific entries. 
I support this Idea!

Nice thought @Nuno Reis .
Agree!..

A much needed one. Thanks

I agree with your idea @Nuno Reis. Good thought

Definitely a much-needed improvement.

@Nuno Reis  You have my support ~ this is a meaningful and appreciated input.

Agreed, adding a filter like the one in the Activity tab would make the Achievements section much more manageable and user-friendly. 

Much appreciated enhancement.