score:1

Accepted answer
var appusers = await _masterdbcontext
    .users
    .asnotracking()
    .include(x => x.usercustomers)
    .where(user => 
        !user.isdeleted 
        && user.usercustomers
            .any( x => x.customerid == tenant.id ) )
    .distinct()
    .select(appuserdto.projection)
    .todatasourceresultasync(request.gridoptions, cancellationtoken: cancellationtoken);

score:0

var filtered = _masterdbcontext.users
    .select(appuserdto.projection)
    .where(user => !user.isdeleted && user.usercustomers.any(x => x.customerid == tenant.id && x.userid == user.id));

var query = 
    from d in filtered.select(d => new { d.id }).distinct()
    from u in filtered.where(u => u.id == d.id).take(1)
    select u;

var appusers = await query.todatasourceresultasync(request.gridoptions, cancellationtoken: cancellationtoken);

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