@courtney pk24816854 – I don't usually script in Bridge, however, I was able to hack the following script together... If you have multiple thumbs selected, then there will be a separate alert for each image. Look for "Keyword Count Alert" in the Tools menu.

// v1.0, 20th January 2023, Stephen Marsh
// Script hacked from:
// How to limit the number of keywords in Bridge
// https://community.adobe.com/t5/bridge/how-to-limit-the-number-of-keywords-in-bridge/m-p/10945147
#target bridge
if (BridgeTalk.appName == "bridge") {
keyCount = MenuElement.create("command", "Keyword Count Alert", "at the end of tools");
}
keyCount.onSelect = function () {
try {
if (ExternalObject.AdobeXMPScript == undefined) ExternalObject.AdobeXMPScript = new ExternalObject("lib:AdobeXMPScript");
var sels = app.document.selections;
for (var a = 0; a < sels.length; a++) {
var thumb = new Thumbnail(sels[a]);
var md = thumb.synchronousMetadata;
var xmp = new XMPMeta(md.serialize());
if (!xmp.doesPropertyExist(XMPConst.NS_DC, "subject")) continue;
var keys = [];
keys = getArrayItems(XMPConst.NS_DC, "subject");
//////////
alert(thumb.name + " = " + keys.length + " keywords");
//////////
function getArrayItems(ns, prop) {
var arrItem = [];
var items = xmp.countArrayItems(ns, prop);
for (var i = 1; i <= items; i++) {
arrItem.push(xmp.getArrayItem(ns, prop, i));
}
return arrItem;
};
}
} catch (e) {
alert(e + "\n" + e.line);
}
};
Tested in versions 2022 and 2023 on the Mac.