First things first. InfluxDB is not and cannot be your recorder DB. HA does not have the ability to use InfluxDB as its recorder. You can use the InfluxDB with Grafana to store long term data for trends and home data, but it will not be readable by HA.
Now that said, there is a way to push data from HA into an InfluxDB. Others have done it. It will not necessarily decrease the reads/writes to your SD card though because you still have to initially store the data in a DB for HA.
So let’s break things down. To reduce wear on your SD card, you want to move your recorder DB off your HA instance. This means installing MariaDB or MySQL on a separate machine (your NAS) and link HA to it. This is different than the MariaDB add-on in HA supervised.
Once your recorder DB is off your RPi, you then want to configure it properly. Things like your recorder configuration should record everything, but for a short amount of time (3 days, 7 days, etc). But history and logbook should be configure to show just the things you care about (motion, door, lights, switches, etc). These are the logbook and history built into HA (side menu) and when you click on an entity to bring up its card.
Now for configuring InfluxDB, I have not done it yet, but others have. You configure InfluxDB to grab everything out of your recorder DB (which is why you want to record everything in the first place). I believe then you can filter what you want to actually store long term. Combine this with Grafana and you have a fairly powerful home history trend and insight.
Now since you have a DS918+, this supports docker. You could theoretically run everything you do now on your RPi, but on your NAS (make sure you have enough memory). HA in a docker, MariaDB in a docker, InfluxDB and Grafana in a docker. and anything else you run (assuming you have HA Supervised on your RPi) as an add-on can be run stand alone as a docker on your NAS and linked to HA through an integration. This will absolutely save your RPi SD card because at this point, you won’t be using it anymore. just take a look at my setup (signature), I run everything in docker on a 6 year old NAS with 8GB memory. Plus then backups and troubleshooting might be easier. I’m not saying you have to change your setup. If you’re comfortable with how you have it installed now and just want to change a few things, that’s fine. I’m just showing options given the hardware you have, direction you say you want to go, and my experience.