Does Ubuntu Mate 22.04.1 [up to date updates] still support legacy mode boot?
About 3 days back after an update my [7 year old desktop PC with an MSI B150M-Night Elf motherboard] stopped booting and I had to resave the CMOS to get it to boot again.
What I did not notice at that time is that is that the boot sequence facility in the CMOS had been deactivated so I cannot boot from a USB memory stick. [or anything else eg. CD ROM]
Before I start looking at other possible causes can you please confirm that legacy boot is supported.
All releases of Ubuntu-MATE will install & boot on legacy hardware.
eg.
I used a 2006 HP Compaq dc7700 in QA-testing installs today for the so-far unreleased Ubuntu-MATE 22.04.2 ISO as shown here and elsewhere.
hp dc7700 (c2d-e6320, 8gb amd/ati rv610/radeon hd2400 pro/xt)
This applies with all releases, and I still use devices that pre-date uEFI; with a current focus of mine being the 22.04.2 we're due to release in what I hope will be mere hours.
Note: that box has had RAM upgraded many times since its original 512MB, CPU upgraded, along with video card (until recently it used an Nvidia card) so its not the same specs as it was sold with in 2006; but no upgrades impacted booting.
I mostly use refurbished laptops, I always use legacy boot, and have not had any trouble.