The basic problem is likely that you are attempting element-wise comparison of character vectors of different sizes using EQ. That won't work.
One solution is to replace this code:
if CRD2020(j).Region == a
Filter(:,j)=1;
elseif CRD2020(j).Region ~= a
Filter(:,j)=0;
end
with this:
if strcmp(a,CRD2020(j).Region)
Filter(:,j)=1;
else
Filter(:,j)=0;
end
or even better with just this:
Filter(:,j) = strcmp(a,CRD2020(j).Region);
Note that you should simplify your code by thinking in terms of arrays (not in terms of loops like some poor low-level language). For example your whole code reduces down to e.g.|:
R = extractfield(CRD2020, 'Region');
a = input('Enter REGION ABV (e.g. UK, KSA etc..): ','s');
F = strcmp(R,a);
