Your other option is to contact Cosmote and see if the customer support staff can activate your number for 5G. I didn’t bother because I had easy access to a TP-Link NX510v (which at the time was the only 5G broadband device on their approved list).
My experience (outside Greece) is that some operators setup SIMs so they only work in particular types of device (e.g., a data only SIM won’t work in a phone and visa versa). Unless you are very convenient to a Cosmote store (I’m not) you might be wasting your time and worth trying to contact them first.
Do let the forum know how you get on. Cosmote has a great 5G service and it is a pity that they don’t have a more permissive approach to 5G broadband equipment.