But how is it possible to keep the wallet unlocked and switch off the PC? My peercoin wallet always needs to be unlocked for minting after I restarted my PC/the wallet, so I assumed it has to be on for a whole year and that would not be worth it, right?
It is not possible to have your wallet running, locked or unlocked, with your PC off, No. Of course not, you're correct in that.
You do not have to leave it on nor staking all year or all the time your computer is running, No. But it could sit in the background running all the time if you choose, yes. This way you are always synced and always helping the EverGreenCoin network.
It would be worth it, Yes. Depending on your balance. But so would staking once a month or less often.
Sorry if I miscommunicated any of the above.
Stake when it is convenient for you or stake all the time. Thank you for doing so, but the decision to "how often?", is yours. Your installments will adjust to gaps in time.