Both Apple and Microsoft have their own Internet Web Browsers, built in as part of their Operating Systems, Mac IOS and Windows and I believe that the same is true of Google, but I have no experience of using that operating system so I can not comment on that.
I know that for many Linux Distributions the first choice that comes with them is FireFox, but it is not built into them and is an application added to the Distribution. Again, I need to qualify this statement by saying I only really have experience of Linux Mint, which is a very popular Linux Distribution, however many of the others seem to have it included as well.
If you do a search on the internet for a browser, you will soon discover that there are a lot of them. I do not know how many there are, but it could well be 100s if not higher than that. You will also see that nearly every site you visit has a favourite browser which makes it very hard to choose an alternative browser.
So why would you choose an other browser? The simple answer is, just as a back up to your main browser in case of problems with it, you might not like the browser you have installed or for any other reason of which there are many. Really the second browser is a matter of personal choice, because the various claims about the browsers, I really do not know if they are correct or not.
FOR IOS
Safari, which is built in with IOS is a very good browser, easy to use and as far as I know as secure as it can be. It is updated regularly and security updates often (along with IOS) often need no action as they are done automatically by Apple. It is important to keep your system updated which will include Safari updates. I like the lay out of Safari and feel very comfortable using it. Saving favourite sites is easy to do. The only problem I have had with it has been with Facebook which is resolved by restarting Safari.
Both Google Chrome and Firefox work well IOS, my personal preference is Firefox. Why Firefox? It has been going since 2004 and I first used it then on Windows, it is the one browser that I keep going back to no matter which operating system I have used. Firefox works well with Mac IOS. The best thing with Firefox is that you can Block AI enhancements, which is something I have done when using it and it works as far as I can tell. Other browsers which are "forks" of Firefox, you can use them, if you can find the installer, however I would not bother to do so because they tend to work better with Windows or Linux.
FOR WINDOWS
My first choice if using windows perhaps would be Edge, because of it being built in with it. The times that I have used it since when using a Windows PC have been good and that is why I recommend it. My other recommendation, if you do not wish to use Google Chrome or Chrome based browsers would be Palemoon it is a very good browser to use and I am surprised it is not more popular. There are so many browsers that work okay on Windows and everyone will have a favourite one. I am not here to tell you which to use only to say from personal experience these are the ones I like.
FOR LINUX
I really do not know with this, because of my limited experience with Linux, only that from those that I have looked and used Firefox is included with them, so I would think that would be for a good reason for the makers to have done so.
OTHER BROWSERS WORTH CONSIDERING
I can again only think about those that I have used and that has been mainly on Windows. Vivaldi is a very good browser as it is very different to most others. I have not used it on IOS so I can not comment on how good it works here. With the newer browsers Brave is interesting, I found it works well, but there is the nagging about Brave Rewards. DuckDuckGo is another browser worth considering. I have liked it when I have used it and will be interested in how it develops which given the way the search engine should be very good.
Points to remember
What ever browser you choose you will have to do some setting up and make some change too. Some, I have found easier to do than others, Chrome and Firefox are very easy to do and have many, many add-ons if you want them. Both the pre-installed browsers, have a lot of choice and a lot of changes and extensions for you to choose from. I tend to stick with things as they are, because it suits me to do so.
FINAL THOUGHTS
Every one will have a favourite browser and searching for one, really can be very confusing. It can also take a long time to do a complete search. Remember that many sites have paid content and are not totally reliable. Look at the suggestions, but make up your own mind - Wikipedia will give you more information on the browser and I have found it a good place to check them out. Do not hurry making your choice and remember the best browser for you is probably the one you are using !