As a man (late 20s), I usually get the idea if you break a date, especially if the reason is easily fabricated or demonstrates that I'm not very valuable. Being really tired from the work week is an easy excuse that clearly shows you're more interested in just relaxing alone than spending time with me.

Plenty of men don't get this, but if they can't handle subtlety, you shouldn't be overly concerned about them to begin with. In my experience, even clingy, emotionally obsessive (see inept) men sense that something is wrong when they get canceled on for a bullshit reason. If they get pushy or hopeful about a follow up date, I think you're fine using "maybes" or "we'll sees". That being said, if they call you out directly and you're not afraid of fallout, just saying "I'm not feeling it" is a really fair way to go about cutting things off without being too blunt or too evasive.

Recent real life example, where things took a positive turn when a girl was subtle, and I accepted that:

So, brief summer fling happened to me. The sex was great, but there was family stuff, and the girl seemed a little wary of how well I was getting to know her through the people closest to her, who we were both spending a lot of time with.

She ended up blowing off two dates in one weekend over just feeling melancholy or something along those lines. I politely told her to just reach out to me the next time she felt like being taken out, knowing that she was either done, had found somebody else, or needed space. A couple months go by with no contact, and then I bumped into her at a social event, where we both knew the other person would be there. Sparks flew again, and she made some rehearsed excuses, which I told her were fine, but didn't matter or affect the last thing I'd said to her. We ended up attached at the hip again, and had some light conversations about finding ways to try dating without family and close friends making it feel like a courtship.

I honestly think her white lies in canceling dates were very respectful and tactfully delivered. And I appreciated that she made more half truth excuses after the fact. It all allowed us to break away and reengage later with no hard feelings. I think we're still wary of the same things as before, but I think we're only able to address them directly now because we both know that we can behave like adults when communicating subtly. She knows that if she needs space, I won't haunt her phone with endless texts. If she walks away, I'll respect it completely.

There's a sort of contract there, I guess, where she's totally responsible for her own decisions. We both saw people during the interim, and it was rather lucky that we were both single when we reconnected. And if she cancels another date in the same way, the expectation is there that I'll move on rapidly if she doesn't express continued interest. That's healthy for me and for her, at least for now, while things are still new and unlabeled.