If you have a prioritised backlog and you’re working in priority order then there’s not much value in sprints — is there? Sprints provide value when you can’t just churn through tickets one after the other in priority order. Sprint planning is time consuming because sprints are useful when you need to plan.
You could use Linear’s cycles and milestones but you probably don’t need any of that structure if you’re just working ticket by ticket.
I've not looked at Linear - but when I was freelancing I used Pivotal (free account) to just put all my clients' requests into one long queue (I had about 8 clients at any one time).
I put in a very random guess as to the points value of each request - nothing more than "trivial, easy, difficult, bastard-bloody-hell-shit-buckets-difficult".
I had Tracker set to work in "weekly sprints" - but they're not really sprints at all - it's just a unit of measure. Internally it averages the number of points completed over the last three weeks, uses that for an average velocity, then moves the date markers on the "backlog" list to match.
Then, when a client asked when something will be done, I could pretty accurately say "unless something urgent crops up, it will be '18th-24th March'" (where "something urgent crops up" means I insert a story at the top of the queue instead of at the end).
PT automatically adjusts the number of stories that make it into a sprint. They don't really have a concept of sprint actually... it is just average velocity over time and the number of stories that can fit into that average.
If a PM wants to see how adding in just one more feature impacts the schedule, they can just drag the pointed story into the queue and see what gets pushed out to the next week.
If a developer goes on vacation, it is easy to see how that impacts the schedule cause you can subtract their average velocity.
Most people don't understand this killer feature of PT unless they've actually spent a bunch of time using it. It really enables you to do accurate project estimates, if you do it right.
You could use Linear’s cycles and milestones but you probably don’t need any of that structure if you’re just working ticket by ticket.