Trek Mamba 2013. 1x11 upgrade

Possible? Yes. Worthwhile? Probably.

You would need to buy a new rear derailleur, the cassette and the crankset (you may reuse the cranks with a new front cog, the tricky part is to get a good chain line, similar to the one you have now with the middle front cog) and of course a new chain.

Rear Hub is fine, it can accomodate a relatively cheap Sunrace 11-50 11-speed cassette.

The dismounting/mounting work is something you can do, no specific trouble, you will need to have 3 specific tools (for cranks and cassette) which will increase the budget needed of about 50/60 $/£/€.

On one hand, doing this you will spend xxx$/£/€ and get the bike you are familiar with, upgraded to a nice 1x11 speed system and you personally will understand a bit more of bicycle manteinance&co.

On the other hand, I think the Trek Mamba is a entry model with rather standard components, so it may be worthwhile to buy a used mtb for 2 times (or even 3 times) the amount xxx with similar geometry and a 1x11 system already installed ... if the "new" bike fits you, you are good to go, sell the Trek Mamba and you recover a bit of money, otherwise you can be almost sure that you can swap the 1x11 components to your Trek Mamba and viceversa and sell the "new" bike for something around xxx.