You have got some interesting replies, so instead of repeating what the others say, I will give you the advice of installing GrapheneOS and degoogle.
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You can try checking your Chrome bookmarks and the homepage settings for anything unusual. Then check your apps for the same. Other than that, I think a factory reset is probably the best way to deal with it, because if it's actually malware then who knows how far down it's embedded into the system.
You can reset Chrome by deleting al app data and flushing cache. The app does not and cannot.get deleted from non root devices, but it will go back to its stock factory preloaded version. Then you can update it and you have a clean Chrome.
That said Chrome custom tabs can also be used by any application, so check what apps you have, and what apps open themselves frequently in background.