For Linkedin ads you can choose countries and many other critical targeting criteria, it's the only platform out of those mentioned that offers a reliable way to target a B2B audience. Others just don't have the data to do so.
Sukh great insights, but a couple of things that come to mind
Google Ads
PMax is a tricky campaign type since you have little control over which networks your spend goes to - $0.05 CPC suggests that you were bringing low quality traffic that wouldn't convert anyway. Usually it works best for ecommerce, otherwise it can be either a hit or a total miss. Also requires quite a lot of training data to optimize, so not a great choice for smaller scale testing.
$7 CPC actually suggest you might have started to show up for high-quality, but competitive terms. Nothing shocking, but you need a strong product, funnel, and sometimes cashflow to make it sustainable. Also be careful with keywords and match types, since Google can push you into broad keywords that are not relevant to your product.
Meta Ads
As with Google Ads, as low as 2 cents CPC suggests your campaigns weren't optimized for conversions - traffic/engagement/reach objectives will mostly bring you low-quality traffic and won't contribute to business growth in any way.
Overall
Paid ads are not the best way to test anything until you have a solid product or landing page. Until then you can draw wrong conclusions because ad platforms just won't be able to receive any quality conversion signals and use them to optimize.
A test like this doesn't prove that those channels work or don't - it depends on the whole funnel, product, data quality, tracking, and probably some more
