I built one of these back during the january omicron wave (us). Mostly out of 'why not' boredom because I already had a box fan, a roll of duct tape, and a near infinite supply of cardboard from amazon, just had to buy four filters from home depot.

Six months later I have to replace the filters because they are a thick dusty grey. Went from looking like white paper with blue flecks in it to looking like grey jersey/t-shirt fabric. If even a tenth of what it caught was otherwise destined for my lungs then this was a big win.