windows 11 requires that the computer hardware support TCM 2.0 for security. TCM is implemented by the computer BIOS. your computer is too old for TPM 2.0 support. If your computer came with TCM 1.2 support the BIOS may be upgradeable. see the dell website:
while there are hacks to get windows 11 to run on a non TCM computer (google), this is not a supported configuration, so you might as well stick with windows 10.