BIOS : Secure mode vs Legacy mode question


if a computer is setup to Secure Boot and we install Uunbutu Budgie

Question 1 : And after we change the BIOS mode to legacy ( change bios mode) after installation, is it bad ?

Question 2 : Does it change something changing mode once installed ? if it can boot in both mode whichever we take ?

Last Question when both are available, should we choose UEFI over BIOS MODE (Legacy) ?

I am asking that because my UB is slow to boot and once in UB it’s ok… I don’t remember if it was BIOS Mode ( legacy) or UEFI when I installed, I just upgrade the bios to last version to have one less variable, but it’s still slow to boot…