I have been thinking about self-hosting my personal photos on my linux server. After the recent backdoor was detected I'm more hesitant to do so especially because i'm no security expert and don't have the time and knowledge to audit my server. All I've done so far is disabling password logins and changing the ssh port. I'm wondering if there are more backdoors and if new ones are made I can't respond in time. Appreciate your thoughts on this for an ordinary user.
I do IT security for a living. It is quite complicated but not unrealistic for you to DIY.
Do a risk assessment first off - how important is your data to you and a hostile someone else? Outputs from the risk assessment might be fixing up backups first. Think about which data might be attractive to someone else and what you do not want to lose. Your photos are probably irreplaceable and your password spreadsheet should probably be a Keepass database. This is personal stuff, work out what is important.
After you've thought about what is important, then you start to look at technologies.
Decide how you need to access your data, when off site. I'll give you a clue: VPN always until you feel proficient to expose your services directly on the internet. IPSEC or OpenVPN or whatevs.
After sorting all that out, why not look into monitoring?