trying to put a /title or a /tellraw with custom font crashes I`ll leave a resorce for you to check

these are the command(in spanish)

/title @s title [\{"text":"Texto con "}, \{"text":"fuente personalizada","font":"minecraft:pacifico"}]

/tellraw @s [\{"text":"Texto con "}, \{"text":"fuente personalizada","font":"minecraft:pacifico"}]