I cannot open irs.gov - what can I do?

The only one I could do was the reload without blockers - don't know how to do that.

I'm not sure what you mean by that. If you installed an ad-blocking product, that would explain an inability to load various sites. Refer to its instructions.

Some of the information will be redundant but review everything to determine if there is something you may have overlooked.

• Safari is slow, stops responding, quits unexpectedly, or has other issues - Apple Support
• If Safari doesn't load a page or webpage items are missing - Apple Support
• How to install Safari extensions on your Mac - Apple Support
• "Safe Mode": Use safe mode to isolate issues with your Mac - Apple Support. Determine if the problems exist in Safe Mode. Then, restart normally.

If you don't get anywhere, you can use the following procedure to determine if the problem is internal or external to your Mac. Causes may involve your router, your ISP, the DNS Server(s) it uses, or certain user-configurable options.

1. Shut down your Mac.
2. Load macOS Recovery by holding ⌘ and r (two fingers) while you start your Mac with a third finger.
3. At the macOS Utilities screen, release those two fingers.
4. Choose Get Help Online.
5. Safari will launch, but it will lack your bookmarks, favorites, history and other preferences.

Determine if the problem persists while using Safari in that mode. After that, restart your Mac normally, and reply with your observations.

Needless to say, if you are using, or have used at any time in the past, any non-Apple "anti-virus", "cleaning", or "Internet security" products including "banking security", anything at all in that broad category of utterly useless garbage, don't. A lot of things won't work if you do.

In that case the cause is almost certain to be a Safari Extension or similar add-on.

• Open Safari's Preferences > Extensions. If you see any Extensions, one or more of them can be the cause: Change Extensions preferences in Safari on Mac
• Sometimes it helps to remove some or all of Safari's browsing history: Clear your browsing history in Safari on Mac
• Sometimes it helps to remove some or all website data: Manage cookies and website data in Safari on Mac
• A recent Discussion raised the possibility that preventing cross-site tracking caused a website to misbehave: Prevent cross-site tracking in Safari on Mac

Those are just a few suggestions that may lead to a solution, but other causes are possible that can affect operation system-wide. EtreCheck can help track down those potential causes: Using EtreCheck - Apple Community

If you can't open a website in Safari on Mac - Apple Support