In a sense the title says it all, but it perhaps doesn't quite capture the scale of the problem, because data from 2023 suggests 20% of the adult population of Scotland are either not registered to vote at all or are not registered at their current address. Presumably people in the latter category might theoretically be able to vote in some cases but would be much less likely to. So if you can persuade the independence supporters in your life to get registered by the deadline of 11.59 tomorrow night (the 20th), that really is half the battle. Pay particular attention to 16 and 17 year olds, because the 2023 figures suggest *40%* of them were unregistered.
Remember that, as long as people are resident in Scotland, there are very few obstacles to be eligible to vote in a Scottish Parliament or local council election. It's no longer necessary to be a citizen of a Commonwealth country - that rule was changed a few years ago, so Americans, Chinese people, etc, etc can all register to vote by tomorrow night as long as they are resident here. The main group that is still partly excluded is prisoners, but several categories of prisoner can apparently vote - remand prisoners, civil prisoners, convicted but unsentenced criminals, prisoners sentenced for non-payment of a fine, prisoners sentenced for contempt of court, and convicted prisoners serving a term of less than 12 months.
The registration process is apparently fairly quick, although don't leave it until the absolute last minute. The online form can be found HERE.