What's the simplest way to make a genuinely random name selection system using Microsoft tools?

Excel is enough for this. The simplest method is to shuffle the entire list once, then take the first person or first few people. That avoids repeatedly drawing the same entry.

1. Put the participants in column A, with a heading in A1 and one participant per row.
2. In B1, enter Random. In B2, enter =RAND() and fill it down alongside the names.
3. Select the random numbers, copy them, then use Paste Special > Values in the same cells. This freezes the draw so recalculation will not change it.
4. Select both columns together, including the headings, and choose Data > Sort. Sort by the Random column, smallest to largest.
5. The first name below the heading is your winner. For five winners, take the first five names.

Make sure each person appears only once before drawing. If two people share a name, use a participant ID or email to distinguish them rather than removing duplicates by name alone.

Save a copy of the frozen, sorted list as the record of the draw. This also lets you use the next person in order if a replacement winner is needed.

Excel’s RAND uses pseudorandom numbers, which are suitable for ordinary informal draws. It is not a certified lottery system. Power Automate only adds value here if you also need scheduled draws or automatic notifications.