Yes, you can still make a nondeductible IRA contribution today. But you will have to file the 2023 Form 8606 for the nondeductible contribution and send it to your designated IRS office. Be sure to include your address on page 1 of the form and your signature and the date on page 2 of the form.
The conversion would be reported on your 2024 return.
Please see How do I enter a backdoor Roth IRA conversion? for detailed instructions.
Please keep in mind the Backdoor Roth only works if your traditional/SEP/SIMPLE IRAs are empty (don't have pre-tax funds).