I heard that the D-10 visa can now be issued for 1 year and renewed up to 3 times?

The D-10 job-seeking visa has indeed been made more flexible, and the total stay allowed has been extended compared to the past. It is issued and extended in increments (commonly six months at a time) up to an overall cap, so depending on your situation you keep extending rather than getting one fixed long block, and immigration assesses your job-seeking activity and points each time, so keep evidence of your job search. Changing from E-7-1 to D-10 is a recognized path, since D-10 is precisely meant for people who left or finished a position and are looking for the next one, and a former E-7 professional generally qualifies under the points-based job-seeking category. Because the exact issuance length and number of extensions get updated by policy and the specific numbers you heard may have changed again, I would strongly recommend confirming the current rule for your exact case on HiKorea or with the 1345 immigration contact center before you file, so you plan your timeline correctly rather than relying on secondhand figures.