Restart errors aside, though, it seems like various operations are just taking an incredibly long time for you. While some things in Zotero can and will be sped up — database access, in particular, is fairly slow for technical reasons and should be greatly improved in the next major version — the slowdowns are so extreme for you that this seems to be something specific to your setup, since people use much larger database without these problems.
For a laptop that old and with a spinning laptop drive, an 840 MB database likely just isn't going to be usable. Most of that size would be the full-text index, so if you don't rely on full-text searching — which I'd also guess might be too slow to use for you — you could change the settings in Search preferences to 0, use "Clear Index…" in that pane, and then use "Check Database Integrity…" in the Advanced → Files and Folders pane to rebuild the database. Both of those actions will likely take a very long time, but afterwards you should end up with a much smaller database.
Alternatively, if you're fully in sync, you could adjust the Search settings and then close Zotero, move the zotero.sqlite in your Zotero data directory out of the way, and then reopen Zotero and sync to pull down all your data without the full-text content. (You probably also would want to disable full-text content syncing in the Sync pane of the preferences.)
Or you can try simply rebuilding your existing database, either with "Check Database Integrity" or by running VACUUM on zotero.sqlite in an external SQLite tool with Zotero closed. After running for potentially a very long time, that would probably speed things up a bit just by rearranging the data in the database, but I don't know how much of a difference it would make.
Or, of course, you could try transferring your Zotero data directory to a newer computer (or just transferring zotero.sqlite and performing the DB rebuild there and transferring it back). An SSD alone would likely drastically speed things up.
Debug ID D133112611 reflecting very slow restart from Zotero encountering an error and having to close. Maybe some of these data will help the technical improvements. This laptop loads a 441 GB Photos Library in just over 60 seconds (vs. 10-15 minutes for a 841 MB Zotero database), so I don't see how this is a hardware problem. I am the PI on multiple simultaneous projects and I adopted Zotero thinking it was for the professional researcher. (I have tried rebuilding and the bubble doesn't respond.)
Note that full text availability and full text indexing aren't the same thing. You'd still _have_ the full text, you just wouldn't be able to include them in searches.
Beyond that, I think you'll have to believe the person who wrote the software about its hardward requirements. A single 800MB database file isn't comparable to whatever leightweight indexing you need for ~100k photos (which, of course, do not have full text content)
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For a laptop that old and with a spinning laptop drive, an 840 MB database likely just isn't going to be usable. Most of that size would be the full-text index, so if you don't rely on full-text searching — which I'd also guess might be too slow to use for you — you could change the settings in Search preferences to 0, use "Clear Index…" in that pane, and then use "Check Database Integrity…" in the Advanced → Files and Folders pane to rebuild the database. Both of those actions will likely take a very long time, but afterwards you should end up with a much smaller database.
Alternatively, if you're fully in sync, you could adjust the Search settings and then close Zotero, move the zotero.sqlite in your Zotero data directory out of the way, and then reopen Zotero and sync to pull down all your data without the full-text content. (You probably also would want to disable full-text content syncing in the Sync pane of the preferences.)
Or you can try simply rebuilding your existing database, either with "Check Database Integrity" or by running VACUUM on zotero.sqlite in an external SQLite tool with Zotero closed. After running for potentially a very long time, that would probably speed things up a bit just by rearranging the data in the database, but I don't know how much of a difference it would make.
Or, of course, you could try transferring your Zotero data directory to a newer computer (or just transferring zotero.sqlite and performing the DB rebuild there and transferring it back). An SSD alone would likely drastically speed things up.
Beyond that, I think you'll have to believe the person who wrote the software about its hardward requirements. A single 800MB database file isn't comparable to whatever leightweight indexing you need for ~100k photos (which, of course, do not have full text content)