Anything with under 7 million users in the UK is a "smaller" service - so has lighter requirements. See https://ofcomlive.my.salesforce-sites.com/formentry/Regulati...

If it allows unmoderated communications, it might be higher risk. See https://www.ofcom.org.uk/siteassets/resources/documents/onli...

But most of the requirements are stuff that Mastodon services should be doing anyway - responding to complaints, have a code of conduct, have moderators, perhaps use a CDN to filter out CSAM etc. See https://www.ofcom.org.uk/siteassets/resources/documents/onli...

If you're self-hosting purely for yourself, there are no users other than yourself - so no need to worry.