Conceptually, yes the technology was there, although metallurgy likely would have complicated things and manufacturing things at the scale required very much seemed to be the limiting factor.

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En-bloc clips were a fairly old concept, dating back to the 1880s with Mannlicher's magazine design and in regular use by the time of WW1 with designs like the Carcano, Berthier, and Mannlicher rifles. Autoloading weapons had been around for decades as well, and the French in particular had already begun a program to develop a semi-automatic replacement for the Lebel in the prewar period, only for it to fall by the wayside when war broke out. More importantly, the particular method the Garand used for actuating its mechanism - a long-stroke gas piston - was very conceptually simple and had been developed and used in several designs by then.

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In fact, the French did actually introduce a semiautomatic rifle in WW1 that shared a lot of characteristics with the Garand - the RSC Model 1917 and 1918. The RSC 1917 used its own proprietary 5-round en-bloc clip, while the 1918 would use a 5-round Berthier en-bloc, and was loaded via the underside of the weapon by opening the magazine and loading it from the bottom. It was operated by a long-stroke piston in a manner that very much resembling that of the Garand, with the piston arm extending in a somewhat circuitous path along the side and under the gun, and, just like the Garand, the locking mechanism was a rotating bolt. The RSC 1917 was nominally adopted in WW1 and something like 100,000 were made, but it was never introduced in enough numbers to overshadow the millions of bolt actions on the front.

The Garand itself? No. John Garand wouldn't develop the gas-operated, rotating-bolt system he'd use on the M1 until the 1930s.

Semi-automatic rifles? Yes. The technology did exist and some countries, the French in particular, were actively pursuing semi-auto rifles before the war.

Why didn't more semi-auto rifles see service in WWI? That's a massive question I've answered here.

To give a short summary of why more semi-auto rifles didn't see service in WWI:

1. Wartime needs. Although wars often inspire innovation, they can make it hard for those innovations to get anywhere. The massive production demands of the war meant that only a few self-loading rifles were ever made (ten of thousands of self-loading rifles compared to millions of other rifles). It cost more money, took more time, and required highly-skilled labor to build self-loading rifles. When you need to buy more make millions of rifles, buying pricey self-loading rifles wasn't a good option for many nations in WWII.
2. Proprietary or rare cartridges. Many early semi-automatic rifles used rare or unique ammunition like .351WSL, 7mm Meunier (the Meunier rifle), or 6.5mm Arisaka (the full-auto Federov). Usually, these were lower-powered rounds which were used to reduce recoil for the shooter and strain on the action. Given the logistical headaches this caused, many armies opted not to widely-issue self-loading rifles).
3. Reliability issues. Early self-loading rifles were notoriously unreliable. Parts broke. Gas systems got gummed up. Dirt and mud messed up the fine tolerances of the action. This is why you see many early self-loading rifles like the temperamental Mauser M1916 go exclusively into air service use, rather than battlefield use.
4. Operating systems. My longer post has a lot more on this, but the gist of the mater is pretty simple. Making small semi-automatic pistols and sporting rifles was relatively easy. Making a gun that could handle the violence of a full-powered military cartridge was really, really hard. Scaling up the operating system from a semi-auto pistol for use in a rifle didn't really work (Paul Mauser lost an eye trying it), so designers really had to go back to square one, which took a lot of time. That's why it isn't until the 1930s that you see some really respectable semi-auto military rifles like the Pedersen rifle or the Garand designs.

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