journalctl to look at your logs.
I’m thinking you may have multiple internal video cards. Please provide the output of
If you need long term support, you’re not going to get it with 18.04. Once 18.04 support is finished (early next year), there’s really no easy way to upgrade to 20.04 because they use entirely different systems and applications. Also “long term support” is a little misleading as it just means you have less version upgrades, but you can consistently upgrade a long term support version through all the “short term support” versions and into another long term support version. There’s really nothing special about LTS except that it implies old software.