Salesforce has been pushing developers to make the jump from the aura components ui namespace to lightning namespace since Winter ’20 release.
Though one can still continue to work with these components, Salesforce would not support cases created around them beyond May 1, 2021. Also, I do not see the pain in migrating to the lightning namespace.
How to do it? Follow one of the examples for migration.
ui Namespaceui:button<ui:button aura:id="button" buttonTitle="Submit" class="button" label="Click me" press="{!c.handleClick}"/>
lightning Namespacelightning:button<lightning:button variant="base" label="Base" title="Base action" onclick="{! c.handleClick }"/>
Old, but worth it!