@allanfelipe I figured out the problem. It's because Opera is somehow doing memory-heavy writing routine to the History file in the Opera folder. When I deleted the entire (maybe a month-long) History, the file went from 6 Mb to 160 Kb, and the deleting speed dropped to nearly zero. This sort of issue has not been a problem until the start of this year or later, which means Opera has started to employ a new routine that now causes it. I outright ask them to fix it, dammit.

@allanfelipe Or at least they should Read and Reply, well, Here, ya know. I've posted my own complaint about this History issue a month or two ago - and I'm yet to receive a single response that Wasn't "well, then just delete your entire History". Nope, it's Broken (their fault), not Overloaded (my fault). That's literally just dodging the actual problem. Annoys me a lot, mind you.

@allanfelipe It's not "nice", because it forces me to choose between "empty History" and "easily deleting specific entries". And also because the sole reason behind this is some shitty encoding that only got introduced recently in the first place. So, no, not "nice" at all.

@allanfelipe I figured out the problem. It's because Opera is somehow doing memory-heavy writing routine to the History file in the Opera folder. When I deleted the entire (maybe a month-long) History, the file went from 6 Mb to 160 Kb, and the deleting speed dropped to nearly zero. This sort of issue has not been a problem until the start of this year or later, which means Opera has started to employ a new routine that now causes it. I outright ask them to fix it, dammit.

@edvardius
Same problem, more or less. Basically, it looks as if it's writing to the file in some way that overclocks the PC in a way that has never happened before some of the recent updates. So it's clearly a bug, but I don't see the developers caring about it whatsoever. Also, it's a proven fact that it is related to the amount of current History, because I wasn't getting it for a day or less after a clean History wipe, but then it came back at an increasing length with each additional day of History. This is very suspicious and/or very buggy. I suggest the developers to actually address it, instead of deleting my complaints. And yes, this involves editing this post to remove the actual complaint. It's outright dishonest to do so, ya know.

@immamangoman
Nope. Probably the only "solution" is to simply not have any History in the first place, but that's not really a "solution". Funny how nobody even tries solving it beyond deleting History or its file. It feels as if this bug is not being taken care of altogether.

@animemidriff
I know for a fact that it used to work like you want a long while ago (since I also used it like that once in a while). But I'm not sure whether it's a setting issue, or Opera's wise guys decided to simply remove it altogether. All I can confirm is that it used to be here once upon a time, yes.

As of somewhat recently (maybe a month, not sure), manual selective History cleanup became a stupidly annoying chore, because even single-entry deletion takes some 3 seconds per entry, and if I use a Search function to separate a group of entries, their deletion literally makes the entire PC overclock as if it's using up most of my Memory to do so.
Note: This is not caused by me having a months-worth clog of History. I deliberately checked it on a cleanly wiped History, and there was almost no difference, especially for the Search-related nonsense.
Also, Opera is known for years to be a Memory-eater for no valid reason, so I fully suspect it being yet another such bug.