I am trying to install Community on a Optiplex 9010. However, after I click on install, the screen starts filling with unreadable graphic characters. The bios is set to legacy boot from USB drive and I briefly see a “Grub” message before the garbage.
I once had a similar issue, although with an HP system instead of a Dell.
In my case, it helped temporarily to connect the DisplayPort output directly to a monitor with native DisplayPort input (before that I was using a DP-to-DVI adapter, to connect to an ancient Monitor…).
In the end, however, in my case a BIOS update solved the problem completely.
For your case, there are several tips floating around, such as: disabling Secure Boot in the BIOS, trying the installation using a Ventoy USB stick, or performing the installation in UEFI mode.