I have just done a massive refactor of my codebase to use the upgradeable version of the 4.x contracts. You can't easily use those contracts just where you need them in a project and intermingle with OZ standard contracts. You get compiler conflicts all over the place with IERC165 vs IERC165Upgradeable having the same functions. So, I get down to the nugget that triggered the big refactor, which is Proxy.
I am trying to proxy a couple of 1155 contracts and a 721 contract but TransparentUpgradeableProxy and ERC1967Proxy both have stuff I don't need. I'm using role-based access with a centralize AccessController. So I extended Proxy and did the stuff that those Transparent and ERC1967 sub-contracts were doing, and implemented RBAC to match my environment. Now I find that there is no ProxyUpgradeable.
Proxy is not a big contract, so I'll repro the functionality via copypasta, but I'm wondering why it was dropped from the contracts-upgradeable version of the contracts. I see no warnings as to the disparity in the docs, in fact the readme in the proxy folder says most proxies are based on Proxy.