If I use Opera for mobile, can I protect my phone from installing any spyware such as Tinder spy apps and others? I think that there are some persons that would like to monitor my activity online.

What is the model of your WIFI router? The address may vary according to the brand of your router. . I have bought Netgear AC3200 - R8000 Nighthawk X6 Tri-Band (https://themybuy.com/best-wireless-routers/).

It has two default adresses - 192.168.1.1 or 192.168.0.1.

And it comes with a Smart Configuration Wizard about how to install it properly:

Launch a web browser from a computer or mobile device that is connected to your router’s network.
Enter http://www.routerlogin.net or http://www.routerlogin.com.
Note: You can also enter your router’s default IP address (192.168.1.1 or 192.168.0.1).
Enter your user name and password.
The user name is admin and the default password is password. Entries are case-sensitive.
If the default username and password are not working, try other passwords that you might have changed to. Otherwise, a factory reset is needed to restore the router to factory defaults. To perform a factory reset, see How do I perform a factory reset on my NETGEAR router?.
The Basic Settings page displays.
In the upper-left corner of the screen, click Setup Wizard.
The Setup Wizard screen displays.
Select Yes.
Click Next.
The Setup Wizard detects your Internet connection.
Click Next.
The router saves your settings and connects to the Internet.
(Optional) To check if you are connected to the Internet, select Router Status under Maintenance.

Check the same setting tips for your router. I think that they may be similar.

Also, you can try to use Malwarebytes Premium antivirus. I have found a lot of positive feedback and reviews but have not tried it yet.

First of all, can you tell me what antivirus do you use? I have a similar set of extensions and use Norton Antivirus Plus but I do not have any problems. Maybe you should try to switch off all extensions first and see how it will work. Then you can try to start any of the extensions one by one and check. Also, you can try to reinstall Opera, maybe it will help you.