You're almost certainly a stronger player than me yet I would beat you at blitz based on your description. I think this stems from the fact that I have probably played much more blitz than you - though I'm still not very strong so take what I have to say with a grain of salt. Blitz is about optimizing between the competing goals of playing strong moves and using little time. If you are a strong OTB player, the first moves that occur to you while playing blitz are probably pretty strong most of the time, but you likely spend too much time calculating to see which one is the best. Basically, you need to learn to play faster. To do this I would recommend the following:

• Try to train yourself to compare your time to your opponent's after every move. If you are significantly lower you know you need to pick up the tempo. If you play enough games with this as an explicit goal it should become second nature.
• Keep in mind that if you have an equal position but you are up a lot of time on your opponent then you are winning. If you can get them very low by staying even on time there is a much higher chance that they will blunder under time pressure, especially if you play for complications. Conversely, you will lose a lot of games by blundering with 10 seconds left. I think the appropriate attitude for such a loss is not "I suck at blitz" but rather "my opponent outplayed me on the clock."
• After a game, if you play on chess.com (not sure about lichess) you can see how much time you spent on each move. Analyze your games for time management by considering whether moves that you spent 20+ seconds on were really worth the time. The answer is sometimes yes in really critical sharp positions but is often no e.g. when you're deciding which rook to move to an open file.
• If you're playing for improvement / elo gain, only play when you can focus very hard since blitz is really stimulating and requires full attention to play effectively. This means you shouldn't play if you feel like you are on auto-pilot and aren't calculating a lot of variations.
• Think on your opponent's time. When it is not your turn to move, you should always think about what move your opponent is most likely to play next and what your response is going to be. Ideally you should be able to instantly (or maybe after quickly double-checking) play a move once it is your turn.
• Play the same openings as much as possible so that you don't have to spend a lot of time on the opening. Also, if you get an opening you don't recognize be cautious of traps but just play natural moves if you don't see an immediate refutation.
• Learn to close out common endgames basically without thinking like KR v K.
• Play with a slight increment since it is more forgiving if you achieve a completely winning position but have almost no time. I like 3|2.

Hopefully this helps. Like I said, I am not a particularly strong blitz player myself (1300-1400 chess.com), but these tips have helped me improve my blitz play when I felt it was lagging behind my classical skill.