How can i select and delete multiple ole objects in writer

I have 400 ole objects in one writer document and i can’t select and delete multiple objects (just one at a time).

Unfortunately no. This is the type of task that the Navigator is ideally designed for, but the UI for the Navigator currently does not allow selecting multiple entries. The related enhancement request for allowing multiple selections in the Navigator is fdo#54834 (although the wording is heading-specific, the principle is the same).

All I can suggest is, if the file is in ODT or DOCX format, you open the file using an archive manager, and manually remove the objects. The objects themselves are usually stored in sub-directories (one per object), so removing the actual objects in this way is the easy part. The harder part is then cleaning up all the references in the XML (content.xmlin the case of an ODT). The references will all look somewhat like:

<draw:frame draw:style-name="fr1" draw:name="Object1" text:anchor-type="paragraph" svg:width="64.01pt" svg:height="37.56pt" draw:z-index="0">
    <draw:object xlink:href="./Object 1" xlink:type="simple" xlink:show="embed" xlink:actuate="onLoad"/>
    <draw:image xlink:href="./ObjectReplacements/Object 1" xlink:type="simple" xlink:show="embed" xlink:actuate="onLoad"/>

Thanks for your answer !