Only thing comes to mind is: Those replaced crystals may have a different resistive (ohms) or capacitive value (in pF) than the originals which is upsetting something....
I have seen odd issues when I replaced crystals on sensitive electronics when did not use close R and pF ratings.
added: are my eyes bad or is there damage to top side of U16 74f244 ? If not try reseating all the socketed IC's (sometimes just pressing hard on them listening or feeling for a little crunch is enough)....

I have re-checked it in MDA mode and I think it might be a bad ram chip, since some symbols are corrupted.

These are crystal oscillators, not just simple crystals, capacitive value shouldn't matter, imho.
On the other hand, looking at photos of your card on vgamuseum, seems that the right value for the 45MHz is 44.9. Probably not easy to find, and I'm not sure that such a small difference is causing the artifacts/noise.
U16 indeed looks strange on your pic. Other than that, broken traces or even a broken ramdac could be the culprit.
Ramdacs of that era are often interchangeable, so you might try to swap it with one from another board, assuming you have one. Of course, carefully compare the pinouts (again assuming you'll find the datasheets for both...)

Just seen your new reply. Not excluding bad ram, but in VGA mode text seemed OK, and bad ram doesn't cause interference/noise as pictured.

I have also noticed that it is 44.9 MHz, but on the PCB there is a marking '45MHz' so I guess it's really not the problem

Horun wrote on 2022-07-23, 22:35:

added: are my eyes bad or is there damage to top side of U16 74f244 ?

It seems to be a type of light reflection or something, dunno. Desoldered U16 and tested it, and it seems to be good

It was due to a faulty RAM-DAC

Bernkastel7734 wrote on 2022-10-06, 21:31:

It was due to a faulty RAM-DAC

You got this right, few days ago I was looking at VGA chipset datasheet that fact is mentions to do TTL monitor driving, the ramdac is bypassed and is driven directly from VGA chipset and one TTL IC to 9 pin port.

Cheers,

Well, I have checked it with TTL monitor and there is no more garbage on the screen I thought was caused by faulty RAM, so I guess that RAM-DAC was so faulty it somehow made the RAM bad?