Why can’t I login to my iCloud

There is a process that you've likely already used.

Sign in and use iCloud.com - Apple Support

Sign in with your Apple ID - Apple Support

You may also try to sign-in from any web browser to access this.

iCloud (sign in with Apple ID here)

https://www.icloud.com/

[Your Apple ID is what you may have used, to login to this Community.]

For General information, see Site:

iCloud - Official Apple Support

PS: additional instructions + video are linked to

address another possibility; how to resolve this.

Assumes you may have used '2FA security' setting;

and indicates some other ideas, in support page..

Change your Apple ID password - Apple Support

//support.apple.com/100193

IF previous items posted, are not workable, this one might.

[Try them, and again too; in case tiny details went missing.]