This stuff can get pretty geeky and budgets also play a part, so I’ll give you the Janet & John version.
The first thing I would say is that you shouldn’t automatically believe everything these online speed testers tell you, because they are often working on out of date concepts and fail to consider individual objectives.
For example, Pingdom reprimands my sites for not using Gzip, but it has no idea I am using Brotli, which is faster. I’ve had others make recommendations that were only relevant before http/2 and now we even have http/3, so a lot of those “best practices” from the past can actually be counterproductive nowadays, assuming you have a good web host.
In some cases, using a service like Cloudflare is very helpful, however it depends greatly on individual requirements and mainly of use if your site has a global target audience or faces particular security threats. On my own sites I recently ran some tests and found they were very slightly slower with Cloudflare than without it, however this was only the case after moving to a new webhost and the clue was actually in the bandwidth stats at Cloudflare.
Previously Cloudflare was trumpeting that they were saving me around 80% on bandwidth that then dropped to 5%. For a while I wondered if CloudFlare was simply being less helpful, but it works on a system of calculating whether the content is served fastest from the origin server or through their network and seeing the big drop in saved bandwidth was very telling. I don’t care about bandwidth because it is cheap these days.
Previous tests had shown a big speed improvement by using Cloudflare on my old web host almost everywhere, however it was now generally a fraction slower when enabled due to the extra hop and only seemed to gain a minimal advantage in really far flung locations thousands of miles from my customers. Given that there is additional complication involved by running Cloudflare I surprised myself by then removing all but a couple websites.
If we look specifically at your situation as a web designer I am guessing that most of your clients are in your area, so it would probably make most sense for you to have a web host with a data centre that is as close as possible to your clients and reduce latency. Then look for the fastest servers possible using technology like LiteSpeed and Quic.
A solution like Cloudflare can be useful in shouldering heavy loads of traffic that might overload a budget priced shared server, but a Blocs site is massively less demanding on the server than something like Wordpress that makes constant requests to a database and likely to slow down badly under a heavy load, especially in a badly managed shared environment.
Getting back to your initial question if you want free or cheap CDN solution check out Cloudflare. If you are determined to keep server costs really low check out Cloudflare, but for many of us it may actually be better taking a closer look at the choice of webhost and running precise tests based on individual needs.