We have unlike may others no spam problems with contributions, however the spam entry via the contact for got annoying. As well there is no problem with joomla-profile generation as this functionality is disabled.
The "contact form" profile has reCaptcha V2 enabled, however a specific spam bot network seems to be able to emulate human interaction. I say specific as the entries are similar and point to a specific source. I/P blocking does not work as I/P is changing, so I look for other solutions for our NGO.
I found no hint how to add a profile field whose result can be compared with a given value to prevent the form from being sent if false.
I found some honeypot instructions for contribution forms, but are not aware what files need to be modified for the contact form and how such coding may interact with update mechanisms. (over-writing)
So, if you have a tip, I will be glad to follow. Thank you.