Starhub got rid off 500Mbps/1Gbps plan for new users. Existing users can still continue using 500Mbps plan (usually no recontract needed as the price remains the same after contract expires) or 1Gbps plan (may require recontract as the price may go up, check your service requirement).
Starhub 2Gbps plan is a dual 1Gbps plan, similar to M1 2Gbps plan.
https://www.starhub.com/personal/support/article.html?id=IzWmqNLUyB2z3slc37MV16
You can use Starhub/M1 2Gbps plan as two 1Gbps line (two independant network with two routers), or you can use it with a Dual WAN Load Balancing capable router (eg: Asus RT-AX86U Pro, Asus TUF-AX6000 or Asus GT-AX6000) to get >1Gbps with single connection and single network.
I was hopping other ISPs to come out with true 2.5Gbps plan after SIMBA's 2.5Gbps plan. Unfortunately it seems to me that would not happen, since Singtel/Starhub are promoting 5Gbps plan instead. Take note I do not recommend SIMBA 2.5Gbps plan at all unless you use it as a backup line (CGNAT, slow speed, unproven stability, etc).
On the other hand, I think SH/M1 2Gbps plan at S$39 are pretty decent if you want to upgrade from 1Gbps (or if you can not get a good recontract deal for 1Gbps).
Starhub 5Gbps plan at S$45 is also a decent deal even if used as a true 2.5Gbps plan (eg: you can choose to go with the ONT option and then use your own 2.5G capable router)