Ubuntu Upgrade Schedule
Canonical - the company that develops Ubuntu - releases two major versions of Ubuntu every year. One in April, another in October. They're numbered as YY.MM, so the latest version available right now is Ubuntu 24.04.
Three out of every four Ubuntu versions are only supported for 6 months, until the next version is available.
However, the version released in April of every even year, such as this last 24.04, is called a Long Term Support version, supported for 5 years.
For users that prefer stability over having the latest features, Canonical recommends using LTS versions of Ubuntu, and allows upgrades from one LTS to the next.
Canonical also does not recommend you to jump to the newest LTS version as soon as it is released. Major bugs are ironed out in the first point release, (the first point release of 24.04 would be 24.04.1), and only then is an upgrade recommended.
Ubuntu is released in different flavours, with each flavour adding its own choice of desktop environments, default applications and settings. Flavours are maintained by the community, with a select high-quality ones being featured on the official Ubuntu website. The LTS period for these flavours is only 3 years.
Potential Issues With Upgrades
Upgrades can have issues, but you can decline them indefinitely. A perk of owning your computer!
Delaying your upgrade for about a month while keeping an eye out for complaints online is always a good idea.
The Ubuntu 24.04 version brought with it a controversial and inexplicable change - when you try to install certain applications from their APT repositories, it installs them from the snap repository instead. Snaps are infamous for being slow, resource intensive, and having a proprietary server implementation. This is outright deceptive from Canonical.
If you already have software installed as APT, and that app is then being forced into a snap, that transition was problematic with the 24.04.0 release.
There is another issue tangentially related to Y2K.
The initial Y2K bug was that dates were being stored with years being represented with just two digits. This was going to cause issues when we entered a new millenium, and a new date format was needed.
The new format counted date and time as the number of seconds that have passed since January 1, 1970 00:00:00 UTC. This reference time is called the Unix Epoch. The problem with this time format is that this was stored as a signed 32-bit integer, which only has enough digits to represent numbers till 2,147,483,647 - the digit 1 written 31 times in binary. These many seconds since the Unix Epoch is 2038-01-19 03:14:08 UTC.
The resolution is simply to use more digits, a 64-bit integer. The transition from 32-bit systems to 64-bit systems was also influenced by RAM limitations with 32-bit systems. Hardware transition is as good as complete, and software transition is nearing completion. This transition is also tricky with the update to 24.04.0.
Actual Issues With 22.04 -> 24.04.1 Updates
According to Canonical, there were critical bugs in the release upgrader, which is quite ironic. Your software is fine, the upgrader has a problem. Even if the software you are upgrading is 2 years old, you cannot be releasing these updates without testing. Users have reported other issues as well.
Mitigation
Upgrades are currently paused until a fixed version can be released. Even upon that release, make sure to have a recovery media on hand.
A LiveUSB is the most common type of recovery media, allowing you to boot into the computer and access your files that you might want to recover. File integrity can also be strengthened if you have your home directory in a different partition, which ensures that even if your OS partition is completely shot, your personal data is safe.