Well, if the pattern is simple enough it’s just a matter of doing a gauge conversion every time you are given a stitch count.
pattern guage 18 sts = 4in
preferred yarn 22 sts = 4in
Pattern says to CO 100
100sts/18guage = 5.5
5.5 x 22guage = 122.2sts
So, CO 122 or 123 with the preferred yarn.
Which you CO (122 or 123) will be decided by the pattern. Does it need to be an even number or an odd?
Also, is it a repeating pattern where you need a multiple of X? If so, then figure out which multiple of x comes closest to the 122.2 and use that multiple/number of sts. So if you needed multiples of 10 then you would have to use 120 or 130sts. Which you choose would likely depend on how tight/loose a knitter you are.