j'ai ce code :     # Web part Activités du site
    $webPartActiviteDuSite = Add-PnPPageWebPart -Page $pageAccueil -DefaultWebPartType "ContentRollup" -Section 1 -Column 1 -WebPartProperties @{
        title = "Activités du site";
    }

    $jsonContentActivitesDuSite = '{
        "query": {
            "contentLocation": 1,
            "contentTypes": [1],
            "sortType": 1,
            "filters": [
                {
                    "filterType": 7,
                    "value": 4
                }
            ],
            "documentTypes": [99]
        },
        "templateId": 1,
        "maxItemsPerPage": 9,
        "hideWebPartWhenEmpty": false,
        "sites": [],
        "queryMode": "Basic",
        "isTitleEnabled": true,
        "layoutId": "Card",
        "dataProviderId": "Search",
        "displayMaps": {
            "1": {
                "headingText": {
                    "sources": ["SiteTitle"]
                },
                "headingUrl": {
                    "sources": ["SPWebUrl"]
                },
                "title": {
                    "sources": ["UserName", "Title"]
                },
                "personImageUrl": {
                    "sources": ["ProfileImageSrc"]
                },
                "name": {
                    "sources": ["Name"]
                },
                "initials": {
                    "sources": ["Initials"]
                },
                "itemUrl": {
                    "sources": ["WebPath"]
                },
                "activity": {
                    "sources": ["ModifiedDate"]
                },
                "previewUrl": {
                    "sources": ["PreviewUrl", "PictureThumbnailURL"]
                },
                "iconUrl": {
                    "sources": ["IconUrl"]
                },
                "accentColor": {
                    "sources": ["AccentColor"]
                },
                "cardType": {
                    "sources": ["CardType"]
                },
                "tipActionLabel": {
                    "sources": ["TipActionLabel"]
                },
                "tipActionButtonIcon": {
                    "sources": ["TipActionButtonIcon"]
                },
                "className": {
                    "sources": ["ClassName"]
                },
                "telemetryProperties": {
                    "sources": ["TelemetryProperties"]
                },
                "imageOverlapText": {
                    "sources": ["ImageOverlapText"]
                },
                "imageOverlapTextAriaLabel": {
                    "sources": ["ImageOverlapTextAriaLabel"]
                },
                "spWebUrl": {
                    "sources": ["SPWebUrl"]
                },
                "fileType": {
                    "sources": ["FileType"]
                },
                "UniqueID": {
                    "sources": ["UniqueID"]
                },
                "iframeUrl": {
                    "sources": ["iframeUrl"]
                },
                "isVideoItem": {
                    "sources": ["isVideoItem"]
                }
            },
            "2": {
                "column1": {
                    "heading": "Typedefichier",
                    "sources": ["FileType"],
                    "width": 34
                },
                "column2": {
                    "heading": "Titre",
                    "sources": ["Title"],
                    "linkUrls": ["WebPath"],
                    "width": 250
                },
                "column3": {
                    "heading": "Date de modification",
                    "sources": ["ModifiedDate"],
                    "width": 100
                },
                "column4": {
                    "heading": "Modifié par",
                    "sources": ["Name"],
                    "width": 150
                }
            },
            "3": {
                "id": {
                    "sources": ["UniqueID"]
                },
                "edit": {
                    "sources": ["edit"]
                },
                "DefaultEncodingURL": {
                    "sources": ["DefaultEncodingURL"]
                },
                "FileExtension": {
                    "sources": ["FileExtension"]
                },
                "FileType": {
                    "sources": ["FileType"]
                },
                "imageOverlapText": {
                    "sources": ["ImageOverlapText"]
                },
                "imageOverlapTextAriaLabel": {
                    "sources": ["ImageOverlapTextAriaLabel"]
                },
                "Path": {
                    "sources": ["Path"]
                },
                "PictureThumbnailURL": {
                    "sources": ["PictureThumbnailURL"]
                },
                "PreviewUrl": {
                    "sources": ["PreviewUrl"]
                },
                "SiteID": {
                    "sources": ["SiteID"]
                },
                "SiteTitle": {
                    "sources": ["SiteTitle"]
                },
                "Title": {
                    "sources": ["Title"]
                },
                "UniqueID": {
                    "sources": ["UniqueID"]
                },
                "WebId": {
                    "sources": ["WebId"]
                },
                "WebPath": {
                    "sources": ["WebPath"]
                },
                "spWebUrl": {
                    "sources": ["SPWebUrl"]
                },
                "fileType": {
                    "sources": ["FileType"]
                },
                "iframeUrl": {
                    "sources": ["iframeUrl"]
                },
                "isVideoItem": {
                    "sources": ["isVideoItem"]
                }
            }
        },
        "webId": "5291cd20-fe29-4145-b666-d7e2a5d5ffe7",
        "siteId": "05b54d20-62db-46b0-988f-3e62ae7ef6d4"
    }'  

    Set-PnPPageWebPart -Page $pageAccueil -Identity $webPartActiviteDuSite.InstanceId.Guid -PropertiesJson $jsonContentActivitesDuSite

Le titre "Activités du site" ne se met pas en place. Ça reste le titre natif de la web part.