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21.04 is not an LTS with 5 years of support. The latest LTS is 20.04.

True:

Ubuntu 21.04 will be supported for 9 months until January 2022. If you need Long Term Support, it is recommended you use Ubuntu 20.04 LTS instead.

Only every second xx.04, to the best of my knowledge. 20.04 was an LTS release, the next LTS will be 22.04. 21.04 is a standard release supported for 6 months.

Edit: Ninja'd by jpace121, should have refreshed before commenting.

Even if my machine won't boot afterwards?

You'll never have to upgrade it again!