It can be used, but there are risks.

If someone has already registered the trademark, it is a trademark infringement.

And it cannot be confirmed whether the trademark being submitted will ultimately pass the review, so the current investment in use is an unknown investment.

The trademark must be indicated as an unregistered trademark. It should be noted that unregistered trademarks have no trademark rights and can be used by others. In this way, the trademark brand cannot be protected, so it is best to wait until the registration is successful before using the trademark.