Modern web browsers like Firefox, Chrome and Chromium based browsers are getting new features everyday. They also have PWA. Unlike Android, browsers on Windows, MacOS, Linux and BSD don't run inside containers. So, the webapp can gain access to the system more easily.
How are the developers solving these issues?
Secure from what or whom?
Do they encrypt traffic from your system to the destination? Yes, they all do. The encryption used is dependent on the host/server you connect to. The browser will try to connect using the "best" encryption that the host allows. Browsers are frequently updated with new encryption and remove old encryption - and do it faster than most hosts/web sites.
Do you mean where a malicious host can attack your system remotely? Anytime vulnerabilities are exposed that allow this, the browsers update/patch quite quickly.
In some ways, the Android browser is a bigger risk because the phones get software updates from the hardware vendor and sometimes is specific to a mobile carrier. E.g. if you have a OnePlus on Verizon, it might get an update sooner or later than a Samsung on AT&T. And, it will depend on which OnePlus or Samsung you have, because mobile phone companies drop support very quickly.
Whereas on a Windows or MacOS system, OS updates and anti-virus are rolled out quite often and these can sometimes prevent browser malware from escaping.
This answer is a few years old, but it mentions the higher probability of users getting malware than a brower-based attack. Chrome + EMET= How Strong Realistic Protection Against Browser-Based Threats?
