The problem with Labour is that they did not nail their colours to the mast over brexit, because they were so nervous about getting it wrong. It made them look very weak and far too indecisive to govern. This failure has absolutely crippled them. They just can't recover.
Whether you like Boris or not, in the run up to the election the conservatives never wavered in their policy on brexit, which is the single most critical issue the country has faced in our lifetime.
Brexit could have been a disaster, but Borris and co made it very clear where they stood, and if brexit was a disaster, the buck would stop with them. Labour didn't want to upset the many Labour voters who wanted brexit, and also wanted to hoover up a lot of remain voters by offering them some hope that brexit could be stopped with a second referendum. Trying to please everyone totally backfired. They were perceived as being too indecisive, and afraid to upset anyone.
16 months on from the election defeat, they still won't explain their position on brexit, because they want to try and somehow win back the trust of those disgruntled traditional Labour heartland voters.
Until the Labour party stops trying to please everybody, and starts being clear where they stand on divisive issues, their decline will continue. If they still believe that brexit was the wrong decision, and I think most of them do, then they should get fully behind that stance with an understanding that they will lose many of their voters, but will gain new ones. If things start going pear shaped as a result of brexit, Labour would have gained a lot of credibility by being apposed to it from the very beginning.
Right now they're perceived as being too nervous about making a stand, with the risk of being wrong and becoming unpopular. A government like this would be a disaster. Starmer and co have to have the balls to draw up policies that they believe in, and then stake the reputation of Labour on those policies. So what if it fails? Better to shoot for the moon and miss, than to shoot at nothing and hit it every time.