I have a riding buddy who rode 30,000 miles two years in a row and worked up to that with 20,000 and 25,000 mile years. Obviously not every one can do that. He didn't overtrain or get weaker, in fact he got stronger and did some fast GR events, 1200k. IME you can tell if you need a rest day or probably easy week. Simple: you get slower or can't do the efforts you could do last week. In fact, in the normal training process, you look for that. You want to get tired, to get slower, so then you know you've hit your limit and need to rest. Doing that, you'll be stronger after the rest because you exerted yourself to your max. Can't do better than that. It's sorta like lifting weights where you rep until you hit failure, then rest a couple days before you lift again. Failure is the goal with that philosophy.
OTOH we don't need to do that that all-out training. It's a option. We can just do long steady distance every day like my buddy and that will get us stronger, too. "Ride lots" as Eddy said.
Meanwhile, watch your morning resting and morning standing HRs. As long as they stay fairly steady, i.e. they go up and down maybe 4 beats and the difference between then goes up and down maybe 10 beats, fine. But if you're watching your standing HR and it just keeps going up and up to over 20 beats above your resting, you probably need to rest and by that time I think you'd have noticed it in your performance anyway. The morning HR thing is sort of a back-up to failure-to-notice or possibly a reassurance when you're just feeling tired. I know when I'm in a build cycle, my legs hurt every day just walking around - but they don't hurt when I'm on the bike unless I deliberately hurt them with hard efforts. Yeah, that sucks but that's what works for me.
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Results matter