If you have arrived in September 2021, this year you will be considered as non-tax resident in Spain.
As a non-tax resident, you will be subject to tax for the income obtained in this country (for example, for the income derived from work carried out in Spain). The tax rate will be the general rate provided for non-residents, which is 24% or 19% for residents in a UE member state.
It is necessary to check the withholding tax rate that the company has been deducting from your Spanish salary. If it is less than 24% (or 19% in your case as resident in a UE country), you must file a Non-Resident Income Tax return (form 210), to pay the difference between the withholding tax deducted by your company and the 24% or 19% tax as a non-resident in Spain.
The deadline for filing the tax return as a non-resident in Spain is quarterly. You must file form 210 in the months of April, July, October and December, in relation to the income obtained in the immediately preceding quarter.