So do I understand correctly that the Threat Monitor automatically detects bots?
Not in the way you probably think it would. It detects a certain behavior (requesting a lot of pages in short time) and puts a rate limit on it first and ultimately a block for the IP. For everything else it relies on either the API of proxycheck.io or manual configuration. Proxycheck.io detects VPNs, proxies and all sorts of bad actors (which then are blocked by Thread Monitor), so also bots - but only a fraction of the resident proxies that are visiting your forum. It is missing the "intelligence" for that (which is no wonder as no tool currently has that intelligence).
But Threat Monitor enables you to block ASNs as well as whole countries, which is pretty effective. How effective it can be depends from the audience of your forum. If you are mainly serving one or a couple of countries you will have no issue blocking some others completely and this way you get rid of a huge amount of the resident proxies if - by accident - you can block Brazil, Argentina, India, Bangladesh, China, Honkong and Singapore (along with a longish list of others that scrape massively but not in the same league). If you can even block the US: even better. However: There is a price to pay: Obviously no one from these countries can access your forum any more as guest and as a consequence no one from a blocked country will be able to register in your forum. The only issue affects registred members from blocked countries that are not logged in currently - they are blocked like normal guests and therefore can't log in. So your forum members better never log out, if they live in a blocked country (or visit one) or use a blocked ASN.
Logged in users are let through, no matter where they connect from. Same goes for ASNs: There are a lot that you can block w/o any harm as basically nothing but bad actors come from there and there is no collateral damage as long as we talk about datacenter ranges. But if you block the ASN of Cable or DSL providers the same happens as before: Forum members that are already logged in and come from a blocked ASN do come through, but no one else.
Threat Monitor acts basically like a firewall with the advantage not to block logged in users. Pretty brilliant. However: It is a pretty big sword and you can do harm to your audience. Plus you have to find out what to block to be effective with as little collateral damage as possible. This is manual effort and time consuming and needs a bit of knowledge and/or learning. That's why I offered to share my blocking list with you - it will give you a massive kick start.
Also worth mentioning: 1000 Calls per day to proxycheck.io are free, if you need more (and you will almost safely need more) cost money. But it is cheap and money well spent. I do run on the 20k-calls per day plan and this is plenty for my forum.
This add on started as a rate limiter, wich (in my eyes) can be useful, but is not the most relevant bot issue today. Later it evolved into the Firewall-alike tool that it is now. As far as I know it is the only add on that can block ASNs and countries from forum access, so if you want that, there is no alternative (plus it is a good tool anyway).
There is another add-on that claims to dedect bots intelligently:
S
A professional access counter, unique visitors analytics, country flags, Bot Defense
This one started as a statistics widget and evolved into something completely different in very short time. I did not test it as I wanted the abilities of Threat Manager for my forum but I am a little suspicious: It came out of nothing (the first public resource of the developer) and the development speed is too fast for my taste, so I have the suspicion it is massively AI coded. There are
sometimes several feature releases on a single day. The advertising claims made are pretty gigantic (including having detection intelligence) and I don't buy them fully. But again: I haven't tried it. Also, some people seem to have issues with the latest releases. So overall not my first choice, the more as I already use IP Threat manager. Other people's mileage may vary and the developer is very responsive.