You haven't told us what type of job you're referring to. But that "direct/indirect competitors" wording is very suspicious.
In my own field, which is Android mobile software programming, having such a clause would be a deal-breaker for me (unless they were paying me a significant percentage of my regular salary to sit on my ass and do nothing during those 6 months).
If I were you, I would email them and ask them:
What did you mean when you said "direct/indirect competitors"? Can you
provide a list of examples you're talking about.
If they say "Don't worry about it, we won't enforce that." Then, strike that clause off from the contract and ask them to initial the change. Don't ask them for permission. Simply do it and email them the new contract, asking them to initial the change.
Or if they give you a perfectly reasonable interpretation of that clause, then do the same thing. Insert the reasonable interpretation they gave you into the contract, email the contract back to them, and ask them that they initial the change you've just made. But again, don't tell them that you're going to modify the contract, just modify it, and then ask them to review and initial the change (before you sign it).
How normal are agreements like this when signing full time contracts?
Unfortunately, these kind of clauses are very common, even for minimum wage workers such as waiters or supermarket cashiers.
But does that really change anything? Some toxic workplaces are very common. That doesn't mean you should accept such unreasonable and overly broad clauses.
If I do want to switch jobs later on, how would I know if a company is considered a indirect / direct competitor?
You wouldn't. That's the entire point of this clause. It tries to give them power over you (whether it's legally enforceable or not).
It's like they expect you to ask them for permission before you apply to any company.
Is there a legal definition
or is more of a question of opinion? How often do companies actually
pursue legal action because of Non Compete clauses?
The rest of these questions are for an employment lawyer in your specific jurisdiction.
But again, even if the company doesn't sue you, does that really matter? At the very minimum, signing such an overly broad clause would give them the idea that they should be able to harass you and harass your new employer.
And even if they don't know where you're going, they may still find out through the grapevine, or when the new company calls to double-check your employment history.