2. Also...I think the Ukrainians are intentionally targeting the tanks. Tanks in mobile warfare are the most effective weapon against other tanks. IFVs and other lighter AFVs can take out tanks, but BTR videos aside, it's not as easy and far more prone to getting yourself killed. Preserve your own tank force (debatable if that is happening) and let the jerks in a jeep, cyka in a machina, chew up and get chewed up. When it is favorable to you, concentrate your surviving tanks and counterattack. IFVs are going to get rough treatment by tanks, even the older T-72s and T-64s.
edit add: Right now, the tanks are more vulnerable, too. General Mud, the Raputitsa, makes picking them off easier than it will be when everything dries out come late May.
So! Are the Ukrainians selectively killing tanks and preserving a nontrivial portion of their tanks for a larger counteroffensive.
I think this a very interesting point, but only if the Ukrainian forces have enough fuel, ammo and supplies for their armoured and mechanized forces to conduct the offensive. There have been a multiple posts here about the Ukrainian logistics issues.
Earlier in the war, I think the Ukrainian forces had an advantage in logistics with their very successful, numerous ambushes of Russian supply convoys. Russia was busy trying to suppress the Ukr AF and AD. Since then the front has stagnated, which ironically, actually benefits the Russians as they consolidate their gains, take less losses, and proceed to use their advantages in the air, cruise missiles, and artillery to destroy the Ukrainian logistics centers across the country (although I will say Ukraine also has some tactical successes with ther artillery).
And the ability to conduct the offensive, thus far, is in theory only. Witness the current Makariv story. Also so far, the strongest mechanized Ukrainian forces in the Donbas have basically not been able to conduct any offensive action. Advances by the separatists have been slow, but shouldn't the Ukrainians have an advantage against these guys? Instead they are on the back foot. They are trying to push at Izyum to prevent the Russians from the north in cutting off the east but will it be successful? Still remains to be seen.
Down in the southwest pass Kherson to Mycolaiv the Russians look spread thin and the Ukrainians have numbers. Maybe they can push there. The Russians used Kinzhal to hit the fuel depot in that area.
While constricting Mauripol hard, it hasn't cracked yet. I seem to recall a poster claiming Mauripol had fallen in a few hours the first night of the war. That post definitely aged well. I expect it will fall and probably by Sunday, but I thought it would have fallen already. Not yet. Not yet.
Mariupol had 3 Ukrainian brigades: 56th mechanized, 36th Marine Corps, 12th National guard. And then there's Azov paramilitaries who probably number a few thousand. I think maybe not all elements are present, but certainly very substantial numbers to cause a massive headache in urban settings. Mariupol has been entrenched for 8 years basically so no easy fight.