Hey!
Since I live in Germany, I think it would be easy for me to help you a bit & recommend some toys
I also have the same situation as you - I have a hamster who is absolutely terrified of humans, so I therefore can't give him any time in the playpen. I'd recommend having a cage as big as possible (from own experience, I find that the cage needs to be at least 1 square meter to keep a hamster happy without a playpen (mine is only 9600 square meters, but im building a new cage soon). Of course, this isn't a must though, it's just something I've noticed while owning hamsters
So to start, I would recommend adding a lot more bedding if you can, in germany the minimum amount of bedding for a syrian is 25cm! This will also give him something to do
I'd also add more things like flax, dari cobs, millet, etc, (these can easily be bought in a fressnapf or megazoo or somethings, (check the birds section)). This gives your hamster something to do, and encourages natural behaviour.
As for chew toys, they aren't really common to use here. Instead, we use only wooden houses, tunnels, etc, so a hamster can chew those. But if you really want to, you can use apple tree twigs, that you can find in most pet stores.
Pleaseee don't use any plastic toys, but instead cork logs, grape vine pieces, etc (not to meantion that plastic in hamster cages is not seen as good hamster care here (aside from the wheel))
(Ps. Do you speak german by any chance?)
Have a lovely day everyone!