The CB AntiSpam plugin does not allow one to select reCAPTCHA v3:

That looks like a bug with the captcha field not letting you override to reCaptcha v3. Will fix that. You can select reCaptcha v3 globally in CB AntiSpam > Parameters > Captcha > General.

Edit: Confirmed there's a bug in the CB AntiSpam Joomla plugin parameter missing v3. That's not where you configure core CBs captcha though. Core CBs captcha should be set in CB AntiSpam > Parameters > Captcha > General. That plugin is to allow CBs captcha to be used outside of CB. Generally it should just be left as "Same as Global". A fix for the missing dropdown option will be available shortly in latest CB AntiSpam build release.

My recommendation is to edit the CB AntiSpam Joomla plugin and reset it back to "Same as Global". Then do the same for the Captcha field in CB > Field Management. Next go to CB AntiSpam > Parameters > Captcha > General and globally set your captcha mode to whichever you like. You're now back on the default behavior and will be easier to globally adjust the captcha mode.

Note that "Invisible" cannot be created from one's Google reCaptch account.

You absolutely can. Select "Challenge (v2)" and you'll get a second parameter to select what type of v2 you want. Checkmark or invisible. They did not discontinue v2 in any way.

I had to build a work-around using the Honeypot variant. To do this successfully, I set the Captcha field in General Configuration to use the CB AntiSpam plugin. This was guesswork on my part; very little documentation exists in the CB Primer.

I'm not sure what you mean by this. A workaround for what? The built in captcha can be entirely customized in CB AntiSpam > Parameters > Captcha > Modes > Internal. From the noise it generates, to the fonts it uses, to the size, to the characters allowed in the captcha, what questions question based captcha ask, etc..

No worries. I'm here to help. If you've any further suggestions on how we can improve CB AntiSpam to alleviate the spam attacks you've experienced then we'd be glad to consider additional features. I don't currently have a roadmap for the new captcha modes, but they're certainly planned and am always looking for additional modes to add.

Another suggestion might be to look into some service side protections to try and block them before they ever reach your site. That usually just results in blocking IP ranges though or common patterns in form data. There's also services like Cloudflare that can provide some protections.