I am not willing to spend any more of my time on this as 64 and 32 bit isn’t what we’re willing to support in the openHAB project. Feel free to provide a PR that adds Bellsoft, I think there’s even some code leftovers as some older Bellsoft Java used to be in in the past.
I have another approach on updating the system: 2 rpi’s, one holding my stable config and a second one for testing new versions of OS, OH and other software. I’ve put lots of effort in scripting complete installation from scratch and OH config is mainly restored via the thing, item and sitemap (and rule) files. Those files are regenerated based on a script, taking into account my environment (prod or test).. It also allows me to easily promote the test rpi to prod once I’m confident ot’s running stable.
I have also a raspi4. Like written in general here I bought only an additional SD-Card. Created a backup-file of configuration via the openhabian menu, copy the file on my PC. Prepared the new SD-Card with the image for 64-bit Openhabian. Copy the Backupfile on to the SD-Card, edit the file config.txt there (to give the info where the file is located and how it is named), in addition entered there the parameter for my wifi. Than put the SD-Card in the raspery, swiched it on and it prepared all inclusive overtaking my configuration. Really really simple and it worked directly. In Addition with the knowledge - if it do not run for whatever reason I can plugin the old SD-Card. Perfect!
It’s even easier possible.
Use the SD mirroring feature of openHABian (menu 54) for automated sync (= a backup, too).
Upgrade OH in place and if things go badly wrong just exchange the cards to boot from so you get back to your old setup.
Just for the records: I finally tried it to update from 4.2.0 to 5.1.1. Everything seemed to work fine at first. But because I used jsscripting and GraalVM doesn’t have a 32bit port anymore none of my scripts worked and I decided it’s not worth the hassle.
So I have to wait until I have a good reason to get rid of my 32bit Synology.
Why not get a Raspi.