The only solution that I have found so far is to put my handlers in a timeout like this:

chrome.tabs.onActivated.addListener((activeInfo) => {
        setTimeout(() => {
           // The old listener handler moves here
        }, 100);
    });

But there must be a better way, right?

You will still get errors but at least it will work

chrome.tabs.onActivated.addListener(function(activeInfo) {getActivatedTab();});
function getActivatedTab(){
    chrome.tabs.query({'active': true, 'lastFocusedWindow': true}, function (tabs) {
        try{
            if(tabs[0]!=undefined){
            
                console.log(tabs[0].url);   
            }
        }
        catch(err){
            setTimeout(function() {
            getActivatedTab();
            },100);
        }
    })
}

This is a bug in Chrome91, as pointed by @wOxxOm.

This patch is suggested if you are making a lot of calls to e.g. xchrome.tabs.query

const ChromeWrapper = {
  chromeTabsQuery: function (params, callback) {
    chrome.tabs.query(params, tabs => {
      if (chrome.runtime.lastError) {
        setTimeout(function () {
          //console.warn("Patch for xchrome.tabs.query (Chrome 91).");
          ChromeWrapper.chromeTabsQuery(params, callback)
        }, 100); // arbitrary delay
      } else {
        callback(tabs)
      }
    })
  }
}

And then, just replace the instances of

xchrome.tabs.query(...

with:

ChromeWrapper.chromeTabsQuery(...

...Alright, I don't have an really better solution other than setTimeout, as I don't really see where are the message/event posted after the tab done, so what I do is also add a setTimeout to do some "trial and error".

But how I do it is to override the original chrome.tabs.get so that we can have the same experience as we use it as expected way. (And easily to delete this snippet when they finally fix it some day)

Here is my code, cheers

    chrome.tabs.get = function () {
        const orig_get = chrome.tabs.get.bind(chrome.tabs);
        return async function (tabId) {
            return new Promise(
                resolve => {
                    var tryGet = () => {
                        orig_get(tabId)
                        .then(resolve)
                        .catch(() => {
                            // console.log("retry get");
                            setTimeout(() => {
                                tryGet(tabId);
                            }, 50);
                        })
                    };
                    tryGet();
                }
            )
        }
    }();

create separate function outside of chrome.tabs.onActivated.addListener. this way work for me.

function insertScript(tab) {
  chrome.tabs.get(tab.tabId, function (info) {
    console.log(info);
   });
}
chrome.tabs.onActivated.addListener(function (tab) {
   setTimeout(function () {
     insertScript(tab);
    }, 500);
});