People don't understand archive. According to POs leads are lost and restored and not archived / unarchived. Let us restore the mark as lost behavior. As sometimes I am better than a goldfish let us point to this old task from 3 yeas ago: https://github.com/odoo/odoo/commit/69a769fc9994d00060485703aa4307e2c8877fb7. This commit basically reverts that one. It was linked to task ID 20996 that explainedwhy archive / unarchive had to be used for leads as people don't understand won / lot for leads. This commit is linked to task ID 1880051 and PR #26977.