Until my late 20s, I was bad with both pitch and rhythm despite playing guitar for over a dozen years. Then I took singing lessons with a professional opera singer for 9 months, one hour a week.

She stressed how important it was to record myself and listen back, in fact she encouraged me to do it for hours at a time. The immediate reaction the first few days of trying this was "holy crap, not only am I pitchy and can't hear it naturally, I'm constantly slowing down and speeding up like +/- 10bpm."

The experience was so distressing that I tried to quit my next lesson, but she pushed back with "Hey if you can hear it, you can fix it. It won't be tomorrow, or next week, or even next month. It could take a year. Improvement happens little by little. And I guarantee you'll see progress as it happens. But you have to put in the work."

After a few weeks of working up to it, I settled into a pattern of spending ~3-5 hours most weeknights in the darkness of my closet, recording myself playing Beatles songs along with an acoustic guitar into a 4-track. Usually just going back and forth over 4-8 bars of a song for 30 minutes, then 30 minutes another section, really just focusing on a couple songs like that. Toward the end of the session I'd attempt several full run throughs, get super frustrated (over increasingly minor issues), and end the session.

And she was right, by about the third month I was comfortable enough to perform in front of the person I was seeing, and by month five, I could get through a song with barely any mistakes, maybe one out of three chances. By the ninth month, after a 15 minute warmup, I could get through a 3 song stretch with just minor errors, enough not to totally embarrass myself at an open mic night.

At that point I felt I hit my goal and took a break from lessons. Never did an open mic night. Continued practicing a bit in my closest, but after a month or two I stopped as well.

And here 20 years later, my rhythm actually is pretty solid... I've been a consistent bedroom guitarist, and routinely record myself, and sometimes I don't bother with a metronome because it sounds that consistent. That said, I stopped singing and that ability is completely gone. But I am starting a similar process learning classical guitar.

So I go back to that original bit of advice with just about anything I try to tackle now... if you're self-aware of your issues, and can actually critically hear them in a recording, then there is a path forward.

Hmmm. I might have to try that.

But also fwiw I'm so bad at tempo that even my heart can't hold a tempo.

So I'll definitely give it a shot but I'm pretty doubtful I'll ever meaningfully maintain a pace or tempo.

Understood, but to be clear, I felt the same way after I heard how off I was, as if maybe there was something defective with my brain.

Just start small, record 4 bars of something, play it back. Use a metronome to gauge the actual amount of drift. See if you can hear what the metronome is telling you. Try to improve it with a few more attempts, then call it a day.

Try again after a good night's rest. Over time you should be able to naturally feel when you're slowing down or speeding up.

I am the same way. I am a music lover, I am good with pitch, can accurately tune a guitar from new strings to within a few cents with no reference. But I can barely clap along with a metronome for more than a few bars. I have had years of lessons but my lack of rhythm really makes it almost impossible to progress despite putting in a lot of practice. My wife who plays guitar for fun will walk up while I am laboring over a piece that I have been working on for weeks and do a better job after two tries. It’s really demoralising! It feels like most people can do rhythm like walking or breathing, but for me it takes 100% CPU and leaves little for anything else.