Can employer cancel signed offer letter

I recently got offer from SG company and I signed the offer letter. They said they will apply work pass and told me not to resign before work pass is approved. Firstly they applied work permit and it got rejected. So they continue applying EP which is likely to be rejected as I'm only qualify for S Pass. I think they don't apply S pass because of not enough quota.

Now I'm waiting for EP result. I know the rejection chance is 99%. I'm worried about what can happen next if EP got rejected. The offer letter describes company can terminate employment with two month notice or salary. It even contains the join date.

I've been rejected to other interviews since I got offer there. I had prepared so much to move to SG. Can they just cancel the offer letter coz of WP got rejected? During the interview they said they are working from home due to Covid. Is there anything I can do if they cancel the offer letter?

Any offer letter or employment contract depends on you getting a work visa. Without one, they are null and void (no termination/cancellation or notice period needed!). Thus the employer was right to tell you not to resign (or make any other preparations for the move) before you have the visa.
Whether you can work for them from another country is up to mutual agreement with the company - and falls under the other country's laws (not Singapore).