all the "solutions" for quick switch i found didnt work for me so heres my workaround
you can put them one by one in console or go to common\Half-Life\valve\autoexec.cfg and put them there at once
if autoexec doesnt automatically work then go to the console and type exec autoexec.cfg

bind 1 "1slot"
bind 2 "2slot"
bind 3 "3slot"
bind 4 "4slot"
bind 5 "5slot"
bind 6 "6slot"
alias "1slot" "slot1;+attack;wait;-attack"
alias "2slot" "slot2;+attack;wait;-attack"
alias "3slot" "slot3;+attack;wait;-attack"
alias "4slot" "slot4;+attack;wait;-attack"
alias "5slot" "slot5;+attack;wait;-attack"
alias "6slot" "slot6;+attack;wait;-attack"
bind mwheeldown "instnext"
bind mwheelup "instprev"
alias instnext "invnext;+attack;wait;-attack"
alias instprev "invprev;+attack;wait;-attack"

you can use the numbers to ONLY switch to the first slot of the weapon category but you can use mouse to instantly cycle, although keep it in mind it will leave the category if its out of guns to show you

also if you know a better way to do this please lmk