Two ways that marketing users can now access converted leads for editing are:

Find them in the global search result, by entering the lead name or other keywords in the global search box and selecting Leads from the drop-down menu. Converted leads will appear in the search result with a check mark icon next to them.

Utilize a list view where lead status equals Qualified, by creating or modifying a list view on the Leads tab and adding a filter for Lead Status equals Qualified. Converted leads will have Qualified as their lead status and will be visible in the list view. Searching the Recent Records component on the homepage or using Data Import Wizard will not allow users to access converted leads for editing. References: https://help.salesforce.com/s/articleView?id=sf.leads_view_converted.htm &type=5