So, what sources are actually available for options? Apart from the PH, I'm aware of Xanathar's and UA. Then, the setting specific options like the Sword Coast. I'm not familiar with Tashas...
Xanathar's Guide to Everything is the main player options expansion. You seem to be familiar with what's in there options wise so I will just point out that many in the community feel that the spell Healing Spirit is unbalanced. It's fine if used in combat as enemies can break concentration, but the problem is that when used out of combat uninterrupted it is a disproportionate amount of healing compared to other spells of its level.
Elemental Evil Player's Companion is a free to download pdf that accompanies the adventure path Princes of the Apocalypse. Contains elemental themed races and spells. Many of these options went on to be reprinted in other material like Volo's and Xanathar's so that they would be in hard copy form that wasn't an adventure path.
Tasha's Cauldron of Everything is not yet out. But it promises to be the next Xanathar's, that is the next expansion to really focus on more mechanics. So far we have seen new options for customizing races. There were a number of UA playtests related to customizing class features as well and they will hopefully find a home here as they were fairly well received.
There are options scattered around other books but they aren't the primary focus. 5e has shifted it's release schedule to be slower but each release contains a bit of everything.
Volo's Guide to Monsters is primarily a monster book containing new stat blocks as well as lore and ecology information. On the player side it contains only additional races. So if you want to allow it will depend primarily on your setting.
Mordenkainen's Tome of Foes is also a book primarily about monsters both crunch and fluff wise. However, it also contains some player options this time mostly taking the form of subraces of races that already exist in the PHB. You got more elves, duergar, deep gnomes, and variant tieflings.
Then you have the setting specific books. They often have the specific races that appear in that setting (both new and some reprinted from Volo's), as well as setting specific subclasses. But their main purpose is to introduce a setting with all the lore and details you'll need to play in it.
Sword Coast Adventurer's Guide focuses on the Sword Coast in the forgotten realms. Contains some subclasses but they are fairly generic and can be brought to basically any setting with little effort. Of note is that it also contains some new spells, two of which the designers went on to state they feel were mistakes (EDIT: I can't find the quote to back this up, and it looks like neither Mearls or Crawford are very outspoken about these so take this statement with a hefty grain of salt). They are Greenflame Blade and Booming Blade, cantrips that allow the user to make a melee attack and add other effects. If there's anything in any of the supplementary material that is unbalanced I'd say these are the closest to it. A lot of the other spells that play nicer went on to be reprinted in Xanathar's.
Guildmaster's Guide to Ravnica brings a setting from Magic: the Gathering to D&D. Contains new races, some generic like centaurs or loxodons (anthropomorphic elephant people). Others not so generic like Simic Hybrids which are mutant humanoids. Also contains a couple of subclasses.
Aquisition's Incorporated is a guide to running a game in the vein of a popular podcast of the same name. That is it focuses on having your adventure party be structured like a corporate company. Definitely leans more toward a humorous satire tone.
Eberron: Rising from the Last War contains the player options needed to play in Eberron. Races like the warforged and shifter are here. Also notable for containing the first new full class: the artificer.
Explorer's Guide to Wildemount is a book for the setting used in another popular podcast Critical Role. Contains some subclasses based on manipulating time.
Mythic Odyssey of Theros is another Magic: the Gathering setting, this time the ancient Greek inspired Theros. You can probably guess what I'm going to say here by now: contains races and subclasses.