I'm not a lawyer and the best advice is to check everything with a lawyer...that said it sounds like the contract would be covered by Cypriot and (if you're in the south) EU law.
I live in Ireland and these sorts of clauses are pretty standard, but I don't know how enforceable they are...there's a lot of nuance. For example, creating a direct competitor will probably put you on shaky ground as it could be argued that you used company trade secrets to gain an advantage.
If you create something completely unrelated it could come down to whether you used any company resources in the process i.e. a company laptop, company email, worked on the project during work hours etc. But even if you create something unrelated and didn't use any company resources that doesn't mean your employer won't try to enforce the clause which could result in a whole bunch of expensive litigation which you probably don't want to have to deal with.
What I have seen work is discussing any side projects (including open source) you're going to work on with your employer first and get written confirmation that they're waiving their right to enforce this clause. They may have legitimate concerns about what you're doing (is it competing with their business, will it be a distraction from your work etc) that you may have to address. This may not work in every case, but usually does.
Ultimately you need a paper trail to ensure you can prove the project wasn't something your employer was paying you for, but as I said if you anticipate your employer enforcing this clause you probably want to think hard about whether you want to have that fight.