There are attacks against Bitcoin that use "non-standard" transactions i.e. something that would fail to be broadcast by a node but can technically be mined (the thing MARA is advertising) that could dramatically increase the validation that could make it take longer than 10 minutes to validate a block for some smaller machines like a rpi. Like everything though this attack requires the attacker to have enough money to keep this going in perpetuity and while small single board computers are limited to 8gb ram it's not impossible to imagine in just a few years single board computers having 16-32gb of ram to tap into.