Hawzah News Agency – Q: If one remains junub (because of some difficulty) until the morning adhān, can he/she fast the following day?
A: There is no problem if one is performing a fast other than that of Ramadan or its qaḍā’. However, while performing Ramadan fast or its qaḍā’, if one has a lawful excuse for not performing ghusl, then it is obligatory to perform tayammum. If he does not perform tayammum either, the fast is invalid.
Source: https://www.leader.ir/en/book/32/Practical-Laws-of-Islam