Other currencies are working aside from USDT. Can’t contact live support now to raise my concern. Anyone here can confirm if you can deposit using USDT?
I just checked that and unlike you, I could select the desired network from the available options.
The only thing that comes to my mind is that the page hasn't loaded properly for you. Do a hard refresh (Ctrl + F5) and see if that helps solve the problem.

Now it’s working properly. I didn’t do hard refresh since I just try to visit again after your confirmation. It’s just odd that other currency is working except USDT that time.
I tried using different browser but the result is the same. I think they do a quick maintenance on USDT currency by the time I check.
Thanks.