cellfun works on cell arrays, as the name says. You are working with tables. So this command does not match at all.
Color1 = ["Blue"; "Orange";"Purple";"Blue";"Fuschia";"Red"];
LiscensePlate1 = [12569;12897;56783;45231;78999;99999];
t1first = datetime(2021,1,1,0,0,0);
t2first = datetime(2021,1,1,3,0,0);
tfirst = t1first:minutes(35):t2first;
tfirst=tfirst';
cars1 = table(Color1,LiscensePlate1,tfirst)
% Table 2
Color2 = ["Blue"; "Orange";"Purple";"Blue";"Fuschia";"Red"];
LiscensePlate2 = [88888;12897;77777;45231;88999;99999];
t1second = datetime(2022,1,1,2,0,0);
t2second = datetime(2022,1,1,5,0,0);
tsecond = t1second:minutes(35):t2second;
tsecond=tsecond';
cars2 = table(Color2,LiscensePlate2,tsecond);
[match, index] = ismember(cars1.LiscensePlate1, cars2.LiscensePlate2)
cars1(match, :)
cars2(index(match), :)
By the way, the word is "license", not "liscense".